Hearing loss among small-scale metal workers in Dar es Salaam, Tanzania

Hearing loss among small-scale metal workers in Dar es Salaam, Tanzania | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Hearing loss among small-scale metal workers in Dar es Salaam, Tanzania Witness John Axwesso, Israel Paul Nyarubeli, Gloria Sakwari, Bente Elisabeth Moen, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9265588/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 7 You are reading this latest preprint version Abstract Small-scale metal industries may place workers at risk of hearing loss due to noise exposure levels that exceed 85dBA. This cross-sectional study assessed hearing loss among 178 male workers exposed to a mean noise level of 97.9 dBA and 72 male workers exposed to a mean noise level of 76.6 dBA. A structured questionnaire was used to obtain demographic and occupational information. Otoscopic examinations were conducted, followed by pure-tone audiometry performed inside a soundproof booth. Hearing loss was defined as a hearing threshold ≥ 25 dB 3000, 4000, or 6000 Hz in either ear. The prevalence of hearing loss was 90.4% in the high-noise exposure group and 41.7% in the low-noise exposure group. In regression analyses, work duration was significantly associated with hearing loss among workers exposed to high noise levels (OR = 1.51; 95%CI: 1.15–1.59), when adjustment for age, previous occupational noise exposure, leisure time noise, and lifestyle factors. The association was even stronger when the analysis was restricted to workers younger than 44 years (OR = 1.51; 95%CI: 1.20–1.90). These findings provide clear evidence of a strong relationship between occupational noise exposure and hearing loss. Preventive measures are urgently needed to reduce noise levels in metal industries and similar work environments. Health sciences/Diseases Earth and environmental sciences/Environmental sciences Health sciences/Health care Health sciences/Health occupations Health sciences/Medical research Health sciences/Risk factors hearing loss informal sector metal industries noise exposure Tanzania Figures Figure 1 Figure 2 Significance of the study In this study, we found significantly higher prevalence of hearing loss among workers in small-scale metal industries in Tanzania who were exposed to mean noise levels of 97.9 dBA, compared with workers exposed to mean noise levels of 76.6 dBA. An association between years of noise exposure and hearing loss indicates that longer work duration in high-noise environments increases the risk of hearing impairment. These findings highlight the need for preventive measures to protect workers’ hearing in informal sector metal industries in developing countries, where the noise exposure is high. Introduction The association between high workplace noise exposure and the development of hearing loss among workers has been recognized for centuries. Hearing loss is known to be preventable, but despite this knowledge, occupational hearing loss is a very prevalent disease. More focus on this disease is clearly needed [ 1 – 4 ]. Historically, noise-induced hearing loss was described as early as the 18th century among workers engaged in metal hammering, such as copper miners [ 5 ]. Studies suggest that continuous excessive noise levels exceeding 85 dBA during an 8-hour work shift, or repeated exposure to high-intensity impulse or impact noise over many years, can lead to gradual and largely irreversible hearing loss [ 6 – 8 ]. In the metal industry, numerous tools and production processes generate high noise levels, placing workers at an elevated risk of developing hearing loss [ 9 – 11 ]. Hearing loss is a global occupational health problem [ 1 – 3 , 12 , 13 ]. Hearing loss prevalence ranges between approximately 7% and 21% in different populations at various regions of the world, and the mean prevalence among industrial workers in developed countries is 16% [ 1 , 14 ]. For instance, a review study of Chinese studies has estimated the prevalence of hearing loss is 21.3% among industrial workers in the mining and manufacturing sector [ 15 ], while a separate study done among welders in Ningbo, China, found a higher prevalence of hearing loss of 54.24% [ 16 ]. This demonstrates the variation we see regarding the occupational hearing loss. The magnitude of hearing loss is often pronounced in small-scale industries, where the noise levels are high, but engineering controls, administrative measures, and hearing protection devices may be limited. For instance, a study performed among forge industry workers with 15 different job titles in the United States, exposed to noise levels above 100 dBA, found that 82% had significant threshold shifts defined by the National Institute for Occupational Safety and Health (NIOSH) [ 17 ]. In Nepal, a hearing loss prevalence of 30.4% has been reported among workers in small-scale metal industries, with noise levels ranging from 65.3 dBA to 84.7 dBA [ 18 ]. Similarly, a study conducted among oil mill workers in Malysia found the prevalence of hearing loss to be 42.7% [ 19 ]. The prevalence of hearing loss among forging workers in India was 90% [ 20 ]. These findings show that hearing loss is a huge problem in small-scale industries exposed to high noise levels. Similar concerns have been seen in African industries, where, for instance, the prevalence of hearing loss has been reported to 47% in the steel industry in Egypt [ 10 ]. In Ethiopia, hearing loss prevalence among metal workers has been reported to 30.7% [ 21 ], and a study in Botswana has reported hearing loss prevalence to 78% among metal workers [ 22 ]. In Uganda, the prevalence of hearing loss has been reported to 19% among metal fabrication workers in the informal sector [ 23 ]. These findings underscore that hearing loss remains a major occupational health challenge in settings where noise exposure is high, and hearing conservation programs might be lacking. In Tanzania, the prevalence of hearing loss has been documented in large-scale industries, including iron and steel (48%) [ 24 ], textiles (58.5%) [ 25 ], and mining (47%) [ 26 ]. However, empirical evidence from small-scale industrial settings in Tanzania is limited. One study conducted in Dar es Salaam reported a prevalence of hearing loss of 22.5% and 18.6% in two small-scale industrial areas [ 27 ]. Nevertheless, this study was published more than two decades ago, and the current status and magnitude of hearing loss among workers in small-scale metal industries remain insufficiently characterized. Recent studies from Tanzania indicate that small-scale metal fabrication activities generate high noise levels, ranging from 89 dBA to 107 dBA, potentially exceeding the occupational exposure limit of 85 dBA, and thereby increasing the risk of hearing loss. In addition, workers in these industries have no hearing protection devices available [ 9 ]. Hearing loss is preventable when effective control measures are properly implemented [ 1 – 3 ]. However, the continued occurrence of hearing loss in Tanzanian industries suggests persistent gaps in regulatory enforcement and preventive measures in low- and middle-income countries [ 24 , 28 , 29 ]. Hearing loss might be caused by several factors, not only noise exposure. Important predictors related to hearing loss are smoking [ 23 , 30 ], age [ 31 ], alcohol [ 32 ], and work duration [ 21 , 23 , 33 – 35 ]. This study aimed to estimate the prevalence of hearing loss among workers in small-scale metal industries and to compare it with a low-noise-exposed reference group. In addition, we sought to examine the association between duration of work and hearing loss while adjusting for potential confounding factors. The broader purpose of the study is to highlight the growing problem of noise exposure and hearing impairment in contemporary Tanzania, and thereby stimulate discussion on the urgent need for appropriate preventive measures. Methods Study design We conducted a descriptive cross-sectional study among 178 male workers from small-scale metal industries, known to be exposed to high noise levels at work, from January 2023 to September 2023. These workers were involved in manual metal fabrication activities which produce noise levels above 85dBA in Dar es Salaam, Tanzania [ 9 ], and have been part of a previous study on noise and sleep [ 36 ]. In this previous study, a reference group of 72 low-exposed workers was also established. The cleaners worked in a university hospital in Dar es Salaam. The two groups have similar social and economic status, and both groups have physical work tasks all day and during daytime. Small-scale metal industries were exposed to high area noise levels ranging 89 dBA to 107 dBA [ 9 ]. In the previous study, the mean personal noise level was 97.9 dBA among small-scale metal workers and 76.6 dBA among the cleaners [ 36 ]. None of the workers in the metal industry used personal hearing protective equipment [ 9 ]. Description of the metal fabrication process Metal fabrication process is performed in informal small-scale metal industries in Tanzania. The process is commonly known as “ gonga gonga ”. Scrap metal is used as raw material for pans, basins, spoons, dustbins, metal bags, cleaning utensils, water cans, gutters, baking items, cookers, and fencing materials. The workers use hand tools for the production of metal goods that are used in industries and households. The production process includes preparing the metal scraps or iron sheets, sketching it to the required item design, cutting and folding stage, hammering, painting or polishing to produce the final product, and finally sale to the customers. The work takes place during daytime between 0600 and 1900. Description of cleaning activities The low-noise exposed group consisted of cleaners employed by a cleaning company at a university teaching hospital in Dar es Salaam. Their work typically took place from 0500 in the morning to 1600 in the afternoon, under structured supervision. Their main responsibilities consisted of routine cleaning of offices, hospital wards, stairs, corridors, windows, sanitation facilities, and outdoor areas. These workers carried out their duties in a quiet environment during the day, with minimal exposure to machine-generated noise. Study participants We contacted three study sites from the high-noise-exposed group and one study site from the low-noise-exposed group and informed them of the aim of the study. We were given a list of workers and randomly invited 204 workers from the high-noise-exposed group and 72 from the low-noise-exposed group. Three workers out of 204 were excluded from the study as they had worked less than 6 months, one had hyperemia, and three had pus in the ear. Nineteen workers did not consent to participate in the study, and we ended with 178 high-noise exposed workers, with a response rate of 87%. We assessed 72 low-noise-exposed workers for eligibility, and all of them participated in this study, giving a 100% response rate (Fig. 1 ). We estimated the sample size of the participants in this study using the prevalence of hearing loss of 30.4% among workers in small-scale metal industries in metal industry in Nepal [ 18 ]. Open-Epi calculator version 3 was used to calculate the sample size of 276 at 95% confidence level [ 37 ]. The sample size was 72 for low-noise exposed group at 95% confidence level at a statistical power of 99.4% that is based on the normal approximation with continuity correction. The power of the study, using the actual number of participants, was later calculated using G*3.1.9.7 developed by University of Düsseldorf, Germany [ 38 ] Using the observed prevalence of hearing loss among the two groups with a two tailed alpha set to 0.05, the study attained a statistical power of approximately 100%, indicating a high chance of detecting a significant association between exposure and hearing loss. Audiometry Audiometry was conducted by an audiologist in a mobile soundproof booth designed for hearing measurements. The booth was transported to each workplace, where all workers were examined. A sound level meter (Brüel and Kjær, type 2250) was used to monitor the background noise inside the test booth to ensure compliance with the ISO 8253-1:2010 standard [ 39 ]. Workers were informed to avoid exposure to loud noise for at least 14 hours prior to testing the following morning. Otoscopic examination was performed first, followed by pure tone audiometry inside the booth, using a pre-calibrated Interacoustics AD226 audiometer (Interacoustics, DK-5500, Middelfart, Denmark) with Amplivox Audiocup earphones, which have a lower test limit of -10 dB. The test sequence began with 1000 Hz, followed by 2000 Hz, 3000 Hz, 4000 Hz, 6000 Hz, 8000 Hz, 500 Hz, 250 Hz, and then a retest at 1000 Hz, after which the thresholds were recorded on the audiogram. Participants were trained and instructed on the pure tone audiometry prior to the testing. In this study, hearing loss was defined as hearing threshold ≥ 25 dB hearing loss at any of 3000, 4000, or 6000 Hz in either ear [ 40 ]. Questionnaire Assessment Two research assistants interviewed the workers, using a structured questionnaire. The interviews were performed at the workplace, inside the soundproof booth. Information was obtained about sociodemographic variables, including age, gender, and educational status (never been to school/primary education/secondary education/tertiary education and above). Workers were asked to report their work duration in years. They were also asked about lifestyle factors; drinking alcohol (yes/no) and current cigarette smoking (yes/no). Workers were also asked if their parents had hearing loss (yes/no), if they had experienced an ear infection the past year (yes/no), if they had high blood pressure (yes/no), if they had diabetes (yes/no) and if they had used ototoxic drugs such as quinine the past week (yes/no). Moreover, workers were asked if they experienced ringing sounds in the ears (yes/no) and if they were bothered by ringing, roaring, or buzzing in their ears or head when going to sleep (yes/no). In addition, there were questions about previous work in a noisy workplace (yes/no), and if they were living in areas with noise, for example churches, mosques, milling machines, bars, and generators (yes/no). They were also asked if they were engaged in noisy leisure time activities, including visits to discotheques, playing in a band, attending concerts, listening to music with loud volume (yes/no), and were using of ear phones to listen music or phone calls (yes/no). The original questionnaire was in English language and was translated to Kiswahili language and back to English language again. Only very minor adjustments were made in the Kiswahili version after this exercise. Pretesting of the questionnaire was performed before the main study among 20 participants from another company to assess the clarity and quality of the tool. Statistical Analysis Audiometry data were entered in SPSS version 27 and Microsoft Excel. Descriptive statistics were calculated. Comparisons of groups were performed using Chi- square tests or Fischer’s exact test, depending on the expected cell count. An independent t-test was used to compare continuous variables. Due to the high prevalence of hearing loss, relative risk and 95% confidence intervals were calculated using logistic regression analysis. A correlation analysis of age and duration of work was performed by calculating the Pearson’s correlations coefficient. Significance level was set to 0.05. Multivariable logistic regression analysis was used to analyze the association between hearing loss and work duration, while adjusting for other variables known to influence hearing ability including education level, previous work in a noisy workplace, living in areas that have noise apart from work, use of ear phones, engagement in leisure activities, use of ototoxic drugs the past week, current cigarette smoking and drinking alcohol. We did not include presence of chronic diseases (diabetes and high blood pressure) in the analysis, as very few workers reported such conditions. The regression analyses were performed with high-noise-exposed workers only. To control properly for age, we repeated the regression analysis including only high-noise-exposed workers below 44 years [ 41 ]. Ethical Approval Ethical approval (MUHAS-REC-04-2022-1082) was obtained from the Institutional Review Board (IRB) from Muhimbili University of Health and Allied Sciences (MUHAS) and by the Regional Committee for Medical and Health Research Ethics (REK) South-East Norway (No 634637/2023). All participants signed an informed consent, and all information collected in this study was kept confidential. All research was performed in accordance with relevant guidelines/regulations in Tanzania and Norway, and the research was performed in accordance with the Declaration of Helsinki. Results Descriptive characteristics of participants This study involved only male workers (n=250). High-noise-exposed workers were older than the low-noise-exposed workers. More than two-thirds of high-noise-exposed workers (69.7%) had worked for more than six years in the small-scale metal industries, whereas the 95.8 in low-noise-exposed group had worked for less than five years. The two groups were also different in terms of their educational level, their engagement in leisure activities, daily smoking, and the use of alcohol. The two groups did not differ in previous employment in noise exposed workplaces or in their medical history, with the exception that use of ototoxic drugs within a week before the hearing test was more common among the high-noise-exposed (Table 1). Table 1: Descriptive characteristics of high- and low-noise-exposed workers Variable High-noise exposed group (n=178) Low-noise exposed group (n=72) p-value Mean age in years (Standard deviation) 34.4 (9.1) 25.6 (6.2) 0.001 1 No (%) No (%) Age group in years 0.001 2 18-35 103 (57.9) 67 (93.1) 36-43 48 (27.0) 3 (4.2) 44-59 27 (15.2) 2 (2.8) Education level 0.001 2 Primary school and below 137 (77.0) 25 (34.7) Secondary school and above 41 (23.0) 47 (65.3) Duration of work in years 1-5 54 (30.3) 69 (95.8) 0.001 2 6 and above 124 (69.7) 3 (4.2) Previous work in noisy workplace 78 (43.8) 26 (36.1) 0.263 2 Current living in areas with activities that generate noise 60 (33.7) 12 (16.7) 0.007 2 Medical history Parents with hearing loss 19 (10.7) 8 (11.1) 0.920 2 Previous ear infection 21 (11.8) 10 (13.9) 0.650 2 High blood pressure 9 (5.1) 1 (1.4) 0.163 3 Diabetes mellitus 5 (2.8) 3 (4.2) 0.418 3 Use of ototoxic drugs 9 (5.1) 0 (0.0) 0.044 3 Lifestyle * Engaged in leisure activities 43 (70.5) 18 (29.5) 0.02 2 Use of ear phones to listen music or phone calls 102 (57.3) 50 (69.4) 0.075 2 Current cigarette smoking 43 (24.2) 9 (12.5) 0.04 2 Drinking alcohol 42 (23.6) 7 (9.7) 0.01 2 Self-reported tinnitus Experience ringing sounds in the ears 35 (19.7) 7 (9.7) 0.057 2 Bothered by ringing, roaring or buzzing in your ears or head when going to sleep 25 (14.0) 4 (5.6) 0.041 3 1 Independent samples t -test for continuous variables, 2 Chi-square test for categorical variables, 3 Fisher’s exact test between high and low noise exposed workers. SD: Standard Deviation. *Leisure activities include visiting discotheques, playing in a band, attending concerts and listening to music with loud volume. Hearing loss high- and low-noise-exposed workers High-noise-exposed workers were 2.17 times more likely to develop hearing loss compared to the low-noise-exposed workers. Workers aged 18-35 were more likely to develop hearing loss compared to other age groups among the high noise exposed workers (Table 2). Table 2: Hearing loss among high-noise exposed workers and low-noise exposed workers Variable High-noised exposed group (n=178) Low-noised exposed group (n=72) RR (95%CI) * Hearing loss 161 (90.4) 30 (41.7) 2.17 (1.64-2.86) Hearing loss by age 18-35 87 (84.5) 26 (38.8) 2.18 (1.58-3.00) 36-43 48 (100.0) 2 (66.7) 1.50 (0.82-2.73) 44-59 26 (96.3) 2 (100.0) 0.96 (0.88-1.00) Hearing loss by duration of exposure in years 1-5 41 (75.9) 28 (40.6) 1.87 (1.31-2.67) 6 and above 120 (96.8) 2 (66.7) 1.45 (0.98 -2.15) Hearing loss by tinnitus 32 (91.4) 4 (57.1) 1.60 (0.88-2.91) Hearing loss was defined as hearing threshold ≥25 dB hearing loss at any of 3000, 4000, or 6000 Hz in either ear. *RR (95% CI) = Relative Risk and 95 percent confidence interval. Hearing thresholds of both ears among high-noise-exposed and low-noised-exposed workers The hearing mean thresholds were slightly higher (worse) in the left ear than in the right ear, with the largest significant differences at 4 kHz ( Figure 2). Logistic regression analysis of hearing loss and work duration Using a multivariable logistic regression analysisamong the high-noise-exposed workers only, hearing loss was significantly associated with longer work duration in the high-noise-exposed workplaces (OR=1.22; 95% CI 1.08-1.38). The association was even stronger when adjusting for previous work in a noisy workplace, living in a noisy area, being engaged in noisy leisure activities, education level, use of ototoxic drugs, smoking, alcohol consumption, and previous ear infection (OR= 1.35; 95% CI 1.15-1.59) (Table 3). Age and work duration were strongly correlated (Pearsons’s correlation coefficient 0.775), and an additional analysis restricted to workers younger than 44 years (n=151) was performed. The results showed a similar significant association between work duration and hearing loss (OR=1. 51; 95% CI 1.20-1.90), when adjusting for the same factors as in the first multivariable regression analysis (OR= 1.51; 95% CI 1.20 -1.90) (Table 4). Table 3: Multivariable logistic regression analysis of hearing loss and work duration among high-noise-exposed workers (n=178) Crude OR (CI) p-value Adjusted OR (CI) p-value Hearing loss Work duration in years 1.22 (1.08-1.38) 0.002 1.35 (1.15-1.59) 0.001 Previously worked in a noisy workplace- No 1 1 Previously worked in a noisy workplace-Yes 2.76 (0.86-8.84) 0.087 8.86 (1.73-45.48) 0.01 Living in areas that have noise apart from work- No 1 1 Living in areas that have noise apart from work- Yes 4.22 (0.93-19.12) 0.062 10.58 (1.83-61.28) 0.008 Use of ear phones- No 1 1 Use of ear phones -Yes 0.93 (0.34-2.58) 0.894 1.62 (0.41-6.31) 0.490 Engaged in leisure activities - No 1 1 Engaged in leisure activities -Yes 2.43 (0.86-6.84) 0.092 0.08 (0.01-0.46) 0.005 Ototoxic drugs - No 1 1 Ototoxic drugs-Yes 0.34 (0.07- 1.79) 0.203 0.31 (0.03-2.87) 0.300 Current cigarette smoking -No 1 1 Current cigarette smoking - Yes 0.96 (0.30-3.12) 0.949 1.60 (0.25-10.17) 0.620 Drinking alcohol -No 1 1 Drinking alcohol-Yes 0.53 (0.18-1.53) 0.238 0.41 (0.08-2.14) 0.292 Education (Primary school and below) 1 1 Education (Secondary school and above) 0.97 (0.30-3.15) 0.959 6.95 (1.15 - 42.10) 0.035 Previous ear infection-No 1 1 Previous ear infection-Yes 0.38 (0.11-1.31) 0.126 0.16 (0.02-1.21) 0.076 OR=odds ratio; CI= 95 percent confidence interval. Hearing loss is defined as a hearing threshold ≥25 dB at any of 3, 4, or 6 kHz in either ear. *Leisure activities include discotheque visits, playing in a band, attending concerts, or listening to music with loud volume sound. Table 4: Multivariable logistic regression analysis of hearing loss and work duration among high-noise-exposed workers, age below 44 years (n=151) Crude OR (CI) p-value Adjusted OR (CI) p-value Hearing loss Work duration in years 1.29 (1.10-1.52) 0.002 1.51 (1.20-1.90) 0.001 Previously worked in a noisy workplace- No 1 1 Previously worked in a noisy workplace-Yes 3.05 (0.94-9.92) 0.065 9.08 (1.42- 55.99) 0.018 Living in areas that have noise apart from work- No 1 1 Living in areas that have noise apart from work- Yes 4.52 (0.99-20.71) 0.052 12.92 (1.92- 86.89) 0.009 Use of ear phones- No 1 1 Use of ear phones -Yes 1.01 (0.35-2.95) 0.983 1.29 (0.29 -5.69) 0.737 Engaged in leisure activities* - No 1 1 Engaged in leisure activities -Yes 0.45 (1.56-1.30) 0.140 0.05 (0.01- 0.43) 0.006 Ototoxic drugs - No 1 1 Ototoxic drugs-Yes 0.33 (0.60-1.77) 0.194 0.16 (0.01 – 1.88) 0.146 Current cigarette smoking -No 1 1 Current cigarette smoking - Yes 0.86 (0.26-2.85) 0.802 1.25 (0.18- 8.72) 0.822 Drinking alcohol -No 1 Drinking alcohol-Yes 0.48 (0.16- 1.42) 0.182 0.33 (0.06-1.94) 0.221 Education (Primary school and below) 1 1 Education (Secondary school and above) 1.01 (0.31-3.34) 0.987 8.38 (1.23-57.71) 0.031 Previous ear infection-No 1 1 Previous ear infection-Yes 0.58 (0.15 - 2.27) 0.436 0.47 (0.05-4.38) 0.509 OR=odds ratio (OR); CI= 95 percent confidence interval. Hearing loss is defined as hearing threshold ≥25 dB at any of 3, 4, or 6 kHz.in the left ear. *Leisure activities include discotheques visits, playing in a band, attending concerts or listening to music with loud volume sound. Discussion In this study we observed a markedly higher prevalence of hearing loss (90.4%) among metal industry workers exposed to high noise levels compared to a reference group of cleaners who were exposed to low noise levels (41.7%) in Tanzania. A significant association was found between hearing loss and work duration in the metal industry. The prevalence of hearing loss observed in our study was similar to findings from a study conducted among forging workers in India, where 90% of workers demonstrated hearing loss [20]. Likewise, a study among metal workers in Botswana reported a prevalence of 78%, which is comparable to our findings [22]. However, the prevalence of hearing loss in our study was higher than reported in a review study of 8 articles, which found hearing loss rates ranging from 13.8% to 59% among metal industry workers [42]. However, the noise levels were only evaluated in two of these review studies, and it is difficult to compare the results to the studies lacking this information. The differences in hearing loss might be related to differences in noise level exposure. Similarly, a study conducted among metal workers in Ethiopia reported a prevalence of hearing loss of 30.7% [21]. In this study, the noise levels were measured but not reported clearly. The noise levels were reported to be above 85 dB, but details were not given. The noise levels might be at a lower level than in our present study. Furthermore, a prevalence of hearing loss of 47 % was reported in the steel industry in Egypt [10], but here the noise levels were not reported. In addition, a study among workers in small-scale metal industries in Nepal reported the prevalence of hearing loss to be 30.4%, but in this study the workplace noise level was below 85 dBA [18]. Another study from Uganda, among metal fabricators in the informal sector, reported a hearing loss prevalence of 29.2 %, which is lower than observed in our current study. In that setting, the workers were exposed to noise levels ranging from 62 dBA during quieter periods to 108 dBA during peak hours. The comparatively lower prevalence of hearing loss in the Ugandan study might be attributed to lower noise levels, but also to the use of hearing protection, specifically earmuffs, which was used by 44.9% of the workers [23]. In contrast, area noise levels in our present study ranged from 89 dBA to 107 dBA, and no workers used hearing protection devices [9]. In our present study, we found a significant association between work duration and hearing loss in the high- noise-exposed workplaces. Workers with five or more years at work in the metal industry had 1.35 times higher odds of developing hearing loss compared to those with shorter work experience. This finding aligns with a study conducted in Turkey, which reported that longer work duration was a significant predictor of hearing loss. Workers with more than five years of work experience were more likely to develop hearing loss compared to those with work experience 5 years or less [33]. Similarly, a study among metal workers in Ethiopia found that longer work duration at noisy workplaces was significantly associated with hearing loss [21]. Additional evidence also supports the association between longer work duration and increased risk of hearing impairment [34]. Furthermore, another study conducted among workers in metal fabrication workplaces indicated that hearing loss was strongly associated with more than five years of work experience, with such workers having 13.7 times higher odds of developing hearing loss [23]. The workers in the present study were exposed to high noise levels ranging from 89 dBA to 107 dBA, and in addition, they did not use hearing protection devices [9]. This combination might be the reason why the prevalence of hearing loss is more than 90% in these workplaces. The low-noise-exposed group in this study had a much lower prevalence of hearing loss compared to the high-noise-exposed group. This is similar to a study performed among steel and iron industries where the prevalence of hearing loss was high among high-noise-exposed workers compared to low-noise-exposed workers [24]. Based on the noise exposure level, comparison with the reference group and control with potential confounding factors in the present study, it seems likely that high noise exposure has contributed to the high prevalence of hearing loss among the metal workers. This situation may have developed because small-scale industries in the informal sector are not registered in the Tanzania Occupational Safety and Health Authority (OSHA) services, and thus have limited occupational health and safety protections. The lack of work environment control in these industries may hinder preventive measures at these workplaces [9,43]. This is not uncommon in African countries. A review study from 2026, concludes that even though available occupational noise regulations might exist in some African nations, the regulations are not implemented. There are an enforcement challenge and lack of compliance to these regulations, especially in the informal sector [4]. Therefore, there is a need for development of hearing conservation programs, health and safety policies, better legislations, and implementation of prevention measures in developing countries, especially for this informal sector. A key strength of this study is the use of objective, standardized methods in data collection. Age is a well-known cause of hearing loss, but we controlled the age factor in our analyses. In the regression analysis, we did not include age due to its correlation with duration of work. Therefore, we performed an additional analysis restricting the participants to workers younger than 44 years to minimize age-related confounding. Questionnaire data were collected by two trained research assistants, and audiometric testing was performed by one qualified audiologist. Although having multiple data collectors may introduce bias, all personnel were thoroughly trained to ensure consistency. Because permanent, soundproof facilities were not available in the workplaces, audiometry was conducted in a noise-isolated area, using a mobile booth to maintain reliability and accuracy of the hearing assessments. The study employed a cross-sectional study design and it was not blinded. The participants were aware of the study’s purpose when providing consent. Due to the design, we conducted regression analyses to examine the association between work duration among high noise exposed workers and hearing loss. The results showed a strong association between hearing loss and duration of work in high- noise-exposed environments at work. However, the work duration variable was restricted to only two categories. Other variables, such as noise from the home environment, exposure to leisure time music, were just categorized as yes or no. Such variables should be better assessed, using continuous variables in future research. The response rate was high, 87% in the high noise exposed group and 100% in the low noise exposed group. The statistical power was approximately 100%, indicating a high likelihood of detecting a true association and reducing the risk of Type II error, although it does not remove the likelihood source of bias. The small-scale metal workers in this setting were all male. Therefore, only male workers were included in both the high and low-noise exposure groups. This reduced a potential gender-related confounding effect in susceptibility to hearing loss. However, this limits the generalizability of the findings to female workers and the broader population. Future studies should consider including a more a gender-balanced sample. In conclusion, the prevalence of hearing loss among small-scale metal workers with high noise exposure levels was high in this study compared to a low noise-exposed group. An association was found between work duration and hearing loss. The findings demonstrate a strong relationship between occupational noise exposure and hearing loss, which indicates the need of workplace intervention to reduce this problem. Small-scale metal industries should be systematically monitored and regulated to prevent occupational hearing loss among the workers. Development of prevention strategies, including hearing conservation programs, is essential. Extending regulatory oversight and preventive measures to workplaces in the informal sector may further help in protecting workers from high levels of occupational noise exposure. Declarations Acknowledgement The authors thank the administration of the Muhimbili University of Health and Allied Sciences (MUHAS), the Addis Ababa University (AAU), and the University of Bergen (UiB) for providing technical support in the development of this research work. We also appreciate the willingness of workers from the industries and cleaners from the university to participate in this study. Authors contribution WJA was involved in conceptualization, data collection, analysis, and writing of this manuscript. IPN, GHS and SHM were involved in data collection. BEM, SHM, and IPN were involved in the conceptualization of the research. All authors contributed to data analysis, interpretation of the results, and critical revision of the manuscript. All authors have read and approved the final version of the manuscript for publication. Funding information This research work is funded by Norwegian Programme for Capacity Development in Higher Education and Research for Development via NORHED Project Safe work conditions by innovative Research and education QZA-21/0162 (North- South -South collaboration) . Data availability All data used in this study are not available, as there are restrictions from the ethical committees regarding sharing personal information. A minimal dataset is available on request. Conflict of Interest The authors have no competing interests to declare in this research. References Nelson, D. I., Nelson, R. Y., Concha-Barrientos, M. & Fingerhut, M. The global burden of occupational noise-induced hearing loss. Am. J. Indust Med. 48 , 446–458 (2005). Masterson, E. A., Themann, C. L. & Calvert, G. M. Prevalence of hearing loss among noise-exposed workers within the agriculture, forestry, fishing, and hunting sector, 2003–2012. Am. J. Ind. Med. 61 , 42–50 (2018). World Health Organization (WHO). World report on hearing. 3. March, (2021). https://www.who.int/publications/i/item/978924002048 . (accessed 29 March 2026). Khoza-Shangase, K. Occupational Noise-Induced Hearing Loss in Africa: Gaps, Barriers, and Strategies for Effective Prevention. Noise Health . 28 (130), 1–23 (2026). Chen, K. T. & Su, S. B. A review of occupational noise-induced hearing loss: focus on mechanisms and preventive measures. Br. Med. Bull. 156 (1), ldaf020 (2025). Tikka, C. et al. 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E. et al. Noise Exposure and Hearing Loss among Workers at a Hammer Forge Company. Semin Hear. 44 (4), 485–502 (2023). Whittaker, J. D., Robinson, T., Acharya, A., Singh, D. & Smith, M. Noise-induced hearing loss in small-scale metal industry in Nepal. J. Laryngol Otol . 128 (10), 871–880 (2014). Mutthumanickam, G., Supramanian, R. K. & Lim, Y. C. Prevalence and Factors Associated With Occupational Noise-Induced Hearing Loss Among Palm Oil Mill Workers in Selangor. Malaysia Cureus 3 :16(8) (2024). Singh, L. P., Bhardwaj, A. & Deepak, K. K. Occupational noise-induced hearing loss in Indian steel industry workers: An exploratory study. Hum. Factors . 55 (2), 411–424 (2013). Melese, M., Adugna, D. G., Mulat, B. & Adera, A. Hearing loss and its associated factors among metal workshop workers at Gondar city, Northwest Ethiopia. Public Health Front. 10 (2022). (2022). Banda, F. M. et al. Hearing impairment among children referred to a public audiology clinic in Gaborone, Botswana. Global Pediatr. Health . 5 , 2333794X18770079 (2018). Agaba, B., Nakku, D., Nakasagga, E. & Atwine, D. Prevalence, risk factors and knowledge of noise-induced hearing loss among metal fabricators in Mbarara city, Uganda: a cross-sectional study. BMJ Public. Health . 3 (2), e001839 (2025). Nyarubeli, I. P., Tungu, A. M., Moen, B. E. & Bråtveit, M. Prevalence of Noise-Induced Hearing Loss Among Tanzanian Iron and Steel Workers: A Cross-Sectional Study. Int. J. Environ. Res. Public. Health . 16 (8), 1367 (2019). Abraham, Z. et al. Prevalence of noise-induced hearing loss among textile industry Workers in Dar es salaam. Tanzan. Ann. Glob Health . 85 , 85 (2019). Musiba, Z. The prevalence of noise-induced hearing loss among Tanzanian miners. Occupational medicine (Oxford, England). 65 (5), 386–390 (2015). Minja, B. M., Moshi, N. H. & Riwa, P. Noise induced hearing loss among industrial workers in Dar es Salaam. East. Afr. Med. J. 80 , 298–302 (2003). Mbuligwe, S. E. Levels and influencing factors of noise pollution from small-scale industries (SSIs) in a developing country. Environ. Manage. 33 , 830–839 (2004). Moroe, N. F. & Khoza-Shangase, K. Recent advances in hearing conservation programmes: A systematic review. South African Journal of Communication Disorders.1;67(2):1–1 (2020). Li, X., Rong, X., Wang, Z. & Lin, A. Association between Smoking and Noise-Induced Hearing Loss: A Meta-Analysis of Observational Studies. Int. J. Environ. Res. Public. Health . 17 (4), 1201 (2020). Wang, Y. et al. Associations Between Occupational Noise Exposure, Aging, and Gender and Hearing Loss: A Cross-Sectional Study in China. Audiol. Res. 15 , 91 (2025). Qian, P. et al. Alcohol as a risk factor for hearing loss: A systematic review and meta-analysis. PLoS ONE . 18 (1), e0280641 (2023). Aliyeva, A. & Sari, E. Role of occupational factors in noise-induced hearing loss: a single-center real-world data study. Egypt. J. Otolaryngol. 41 , 43 (2025). Mehrotra, A. et al. Prevalence of Noise-Induced Hearing Loss among Truck Drivers: a Cross-Sectional Study in Lucknow. Noise Health . 27 (124), 72–79 (2025). Gopinath, B., McMahon, C., Tang, D., Burlutsky, G. & Mitchell, P. Workplace noise exposure and the prevalence and 10-year incidence of age-related hearing loss. PLoS One . 16 (7), e0255356 (2021). Axwesso, W. J. et al. Relationship Between Workplace Noise Exposure and Sleep in Tanzania. Noise Health . 27 (129), 934–944 (2025b). Dean, A. G., Sullivan, K. M., Soe, M. M. & OpenEpi Open-Source Epidemiologic Statistics for Public Health, Version updated 6 April 2013. Available at URL www.OpenEpi.comaccessed 18 March. (2026). Faul, F., Erdfelder, E., Buchner, A. & Lang, A. G. Statistical power analyses using G*Power 3.1: tests for correlation and regression analyses. Behav. Res. Methods . 41 (4), 1149–1160 (2009). Standardization (ISO) IO for Acoustics-Audiometric Test. Methods—Part1: Pure Tone Air and Borne Conduction Audiometry. ISO 8253-1:2010. https://www.iso.org/obp/ui/#iso:std:iso:8253:-1:ed-2:v1:en . (accessed 29 March 2026). Le, T. N. et al. Current insights in noise-induced hearing loss: a literature review of the underlying mechanism, pathophysiology, asymmetry, and management options. J. Otolaryngol. Head Neck Surg. 46 , 41 (2017). Homans, N. C., Boons, J. H. C. & Goedegebure, A. Hearing loss prevalence in the aging population: updated population-based audiometric data from the Rotterdam study. Int. J. Audiol. , 1–9. (2025). Raphela, F. S. A Systematic Review of Hearing Loss and Its Associated Factors Among Workers in the Metal Industry. J. Otorhinolaryngol. Hear. Balance Med. 6 , 18 (2025). Mrema, E. J., Ngowi, A. V. & Mamuya, S. H. Status of occupational health and safety and related challenges in expanding economy of Tanzania. Ann. Glob Health . 81 , 538–547 (2015). Additional Declarations No competing interests reported. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9265588","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":634947420,"identity":"2289ec77-ce94-417a-8e4e-ff8be9e844df","order_by":0,"name":"Witness John Axwesso","email":"","orcid":"","institution":"Muhimbili University of Health and Allied Sciences (MUHAS)","correspondingAuthor":false,"prefix":"","firstName":"Witness","middleName":"John","lastName":"Axwesso","suffix":""},{"id":634947421,"identity":"7684d0a1-46a7-4d83-8263-7b434d76562d","order_by":1,"name":"Israel Paul Nyarubeli","email":"","orcid":"","institution":"Muhimbili University of Health and Allied Sciences (MUHAS)","correspondingAuthor":false,"prefix":"","firstName":"Israel","middleName":"Paul","lastName":"Nyarubeli","suffix":""},{"id":634947422,"identity":"beba3678-2cd0-4ba8-841e-bacbc4be5e80","order_by":2,"name":"Gloria Sakwari","email":"","orcid":"","institution":"Muhimbili University of Health and Allied Sciences (MUHAS)","correspondingAuthor":false,"prefix":"","firstName":"Gloria","middleName":"","lastName":"Sakwari","suffix":""},{"id":634947423,"identity":"4acd9c27-d693-44a5-9a4a-ef2f64b2d5f5","order_by":3,"name":"Bente Elisabeth Moen","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA00lEQVRIiWNgGAWjYBACewh1GIiZDzAkNhChxbCBgRGo7jmQyZZAnBaDA2At/4FMHgMwk7At7b3HH3xguC3HL93zTeLhDoY8fkJa7HnOJTbOYLhtLDnn7DaJxDMMxZKEbDKckWPYzMNwO3HDjVygljaGxA0HCPnl/hvD5j8MhxP338h5RqSWGzyGzcBATtwgkcNGnBbDnhzDmT0Gh40lbqQZWySekUicScgv9uxnDD78qDgsxz8j+eHNnztsEvsJ6IA5D86SIE7DKBgFo2AUjAL8AABv+EbIx3Xx7AAAAABJRU5ErkJggg==","orcid":"","institution":"University of Bergen","correspondingAuthor":true,"prefix":"","firstName":"Bente","middleName":"Elisabeth","lastName":"Moen","suffix":""},{"id":634947424,"identity":"2c7b2df8-f295-4f7c-bcfc-82cae54ecb4e","order_by":4,"name":"Simon Henry Mamuya","email":"","orcid":"","institution":"Muhimbili University of Health and Allied Sciences (MUHAS)","correspondingAuthor":false,"prefix":"","firstName":"Simon","middleName":"Henry","lastName":"Mamuya","suffix":""}],"badges":[],"createdAt":"2026-03-30 10:39:24","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9265588/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9265588/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":108595321,"identity":"34244023-6b92-45f7-a953-afbad74c784b","added_by":"auto","created_at":"2026-05-06 10:27:29","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":74553,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eParticipants among high- and low-noise-exposed workers\u003c/em\u003e\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-9265588/v1/a3ba4d300c58c84a48c48b07.jpg"},{"id":108595275,"identity":"802a7c01-0983-4ce0-9e6d-6c509d93f26a","added_by":"auto","created_at":"2026-05-06 10:27:23","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":102769,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eMean hearing thresholds (dB Hearing loss) by frequency in high-noise exposed (n=178) and low-noise exposed (n=72) workers, shown separately for left and right ears. Higher values indicate worse hearing\u003c/em\u003e\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-9265588/v1/ac832002cb48a0db4b3916db.jpg"},{"id":108595374,"identity":"e6d8e0a0-614f-4b15-87b9-7ca302d00521","added_by":"auto","created_at":"2026-05-06 10:27:45","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":626696,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9265588/v1/acabb8a5-9cda-4216-bf9c-966534d6e933.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Hearing loss among small-scale metal workers in Dar es Salaam, Tanzania","fulltext":[{"header":"Significance of the study","content":"\u003cp\u003eIn this study, we found significantly higher prevalence of hearing loss among workers in small-scale metal industries in Tanzania who were exposed to mean noise levels of 97.9 dBA, compared with workers exposed to mean noise levels of 76.6 dBA. An association between years of noise exposure and hearing loss indicates that longer work duration in high-noise environments increases the risk of hearing impairment. These findings highlight the need for preventive measures to protect workers\u0026rsquo; hearing in informal sector metal industries in developing countries, where the noise exposure is high.\u003c/p\u003e"},{"header":"Introduction","content":"\u003cp\u003eThe association between high workplace noise exposure and the development of hearing loss among workers has been recognized for centuries. Hearing loss is known to be preventable, but despite this knowledge, occupational hearing loss is a very prevalent disease. More focus on this disease is clearly needed [\u003cspan additionalcitationids=\"CR2 CR3\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eHistorically, noise-induced hearing loss was described as early as the 18th century among workers engaged in metal hammering, such as copper miners [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Studies suggest that continuous excessive noise levels exceeding 85 dBA during an 8-hour work shift, or repeated exposure to high-intensity impulse or impact noise over many years, can lead to gradual and largely irreversible hearing loss [\u003cspan additionalcitationids=\"CR7\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. In the metal industry, numerous tools and production processes generate high noise levels, placing workers at an elevated risk of developing hearing loss [\u003cspan additionalcitationids=\"CR10\" citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eHearing loss is a global occupational health problem [\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Hearing loss prevalence ranges between approximately 7% and 21% in different populations at various regions of the world, and the mean prevalence among industrial workers in developed countries is 16% [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. For instance, a review study of Chinese studies has estimated the prevalence of hearing loss is 21.3% among industrial workers in the mining and manufacturing sector [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e], while a separate study done among welders in Ningbo, China, found a higher prevalence of hearing loss of 54.24% [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. This demonstrates the variation we see regarding the occupational hearing loss.\u003c/p\u003e \u003cp\u003eThe magnitude of hearing loss is often pronounced in small-scale industries, where the noise levels are high, but engineering controls, administrative measures, and hearing protection devices may be limited. For instance, a study performed among forge industry workers with 15 different job titles in the United States, exposed to noise levels above 100 dBA, found that 82% had significant threshold shifts defined by the National Institute for Occupational Safety and Health (NIOSH) [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. In Nepal, a hearing loss prevalence of 30.4% has been reported among workers in small-scale metal industries, with noise levels ranging from 65.3 dBA to 84.7 dBA [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Similarly, a study conducted among oil mill workers in Malysia found the prevalence of hearing loss to be 42.7% [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. The prevalence of hearing loss among forging workers in India was 90% [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. These findings show that hearing loss is a huge problem in small-scale industries exposed to high noise levels.\u003c/p\u003e \u003cp\u003eSimilar concerns have been seen in African industries, where, for instance, the prevalence of hearing loss has been reported to 47% in the steel industry in Egypt [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. In Ethiopia, hearing loss prevalence among metal workers has been reported to 30.7% [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e], and a study in Botswana has reported hearing loss prevalence to 78% among metal workers [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. In Uganda, the prevalence of hearing loss has been reported to 19% among metal fabrication workers in the informal sector [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. These findings underscore that hearing loss remains a major occupational health challenge in settings where noise exposure is high, and hearing conservation programs might be lacking.\u003c/p\u003e \u003cp\u003eIn Tanzania, the prevalence of hearing loss has been documented in large-scale industries, including iron and steel (48%) [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e], textiles (58.5%) [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e], and mining (47%) [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. However, empirical evidence from small-scale industrial settings in Tanzania is limited. One study conducted in Dar es Salaam reported a prevalence of hearing loss of 22.5% and 18.6% in two small-scale industrial areas [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. Nevertheless, this study was published more than two decades ago, and the current status and magnitude of hearing loss among workers in small-scale metal industries remain insufficiently characterized.\u003c/p\u003e \u003cp\u003eRecent studies from Tanzania indicate that small-scale metal fabrication activities generate high noise levels, ranging from 89 dBA to 107 dBA, potentially exceeding the occupational exposure limit of 85 dBA, and thereby increasing the risk of hearing loss. In addition, workers in these industries have no hearing protection devices available [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Hearing loss is preventable when effective control measures are properly implemented [\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. However, the continued occurrence of hearing loss in Tanzanian industries suggests persistent gaps in regulatory enforcement and preventive measures in low- and middle-income countries [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eHearing loss might be caused by several factors, not only noise exposure. Important predictors related to hearing loss are smoking [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e], age [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e], alcohol [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e], and work duration [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan additionalcitationids=\"CR34\" citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThis study aimed to estimate the prevalence of hearing loss among workers in small-scale metal industries and to compare it with a low-noise-exposed reference group. In addition, we sought to examine the association between duration of work and hearing loss while adjusting for potential confounding factors. The broader purpose of the study is to highlight the growing problem of noise exposure and hearing impairment in contemporary Tanzania, and thereby stimulate discussion on the urgent need for appropriate preventive measures.\u003c/p\u003e"},{"header":"Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eStudy design\u003c/h2\u003e \u003cp\u003eWe conducted a descriptive cross-sectional study among 178 male workers from small-scale metal industries, known to be exposed to high noise levels at work, from January 2023 to September 2023. These workers were involved in manual metal fabrication activities which produce noise levels above 85dBA in Dar es Salaam, Tanzania [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e], and have been part of a previous study on noise and sleep [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. In this previous study, a reference group of 72 low-exposed workers was also established. The cleaners worked in a university hospital in Dar es Salaam. The two groups have similar social and economic status, and both groups have physical work tasks all day and during daytime.\u003c/p\u003e \u003cp\u003eSmall-scale metal industries were exposed to high area noise levels ranging 89 dBA to 107 dBA [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. In the previous study, the mean personal noise level was 97.9 dBA among small-scale metal workers and 76.6 dBA among the cleaners [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. None of the workers in the metal industry used personal hearing protective equipment [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eDescription of the metal fabrication process\u003c/h3\u003e\n\u003cp\u003eMetal fabrication process is performed in informal small-scale metal industries in Tanzania. The process is commonly known as \u0026ldquo;\u003cem\u003egonga gonga\u003c/em\u003e\u0026rdquo;. Scrap metal is used as raw material for pans, basins, spoons, dustbins, metal bags, cleaning utensils, water cans, gutters, baking items, cookers, and fencing materials. The workers use hand tools for the production of metal goods that are used in industries and households. The production process includes preparing the metal scraps or iron sheets, sketching it to the required item design, cutting and folding stage, hammering, painting or polishing to produce the final product, and finally sale to the customers. The work takes place during daytime between 0600 and 1900.\u003c/p\u003e\n\u003ch3\u003eDescription of cleaning activities\u003c/h3\u003e\n\u003cp\u003eThe low-noise exposed group consisted of cleaners employed by a cleaning company at a university teaching hospital in Dar es Salaam. Their work typically took place from 0500 in the morning to 1600 in the afternoon, under structured supervision. Their main responsibilities consisted of routine cleaning of offices, hospital wards, stairs, corridors, windows, sanitation facilities, and outdoor areas. These workers carried out their duties in a quiet environment during the day, with minimal exposure to machine-generated noise.\u003c/p\u003e\n\u003ch3\u003eStudy participants\u003c/h3\u003e\n\u003cp\u003eWe contacted three study sites from the high-noise-exposed group and one study site from the low-noise-exposed group and informed them of the aim of the study. We were given a list of workers and randomly invited 204 workers from the high-noise-exposed group and 72 from the low-noise-exposed group. Three workers out of 204 were excluded from the study as they had worked less than 6 months, one had hyperemia, and three had pus in the ear. Nineteen workers did not consent to participate in the study, and we ended with 178 high-noise exposed workers, with a response rate of 87%. We assessed 72 low-noise-exposed workers for eligibility, and all of them participated in this study, giving a 100% response rate (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eWe estimated the sample size of the participants in this study using the prevalence of hearing loss of 30.4% among workers in small-scale metal industries in metal industry in Nepal [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Open-Epi calculator version 3 was used to calculate the sample size of 276 at 95% confidence level [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. The sample size was 72 for low-noise exposed group at 95% confidence level at a statistical power of 99.4% that is based on the normal approximation with continuity correction.\u003c/p\u003e \u003cp\u003eThe power of the study, using the actual number of participants, was later calculated using G*3.1.9.7 developed by University of D\u0026uuml;sseldorf, Germany [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e] Using the observed prevalence of hearing loss among the two groups with a two tailed alpha set to 0.05, the study attained a statistical power of approximately 100%, indicating a high chance of detecting a significant association between exposure and hearing loss.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eAudiometry\u003c/h3\u003e\n\u003cp\u003eAudiometry was conducted by an audiologist in a mobile soundproof booth designed for hearing measurements. The booth was transported to each workplace, where all workers were examined. A sound level meter (Br\u0026uuml;el and Kj\u0026aelig;r, type 2250) was used to monitor the background noise inside the test booth to ensure compliance with the ISO 8253-1:2010 standard [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eWorkers were informed to avoid exposure to loud noise for at least 14 hours prior to testing the following morning. Otoscopic examination was performed first, followed by pure tone audiometry inside the booth, using a pre-calibrated Interacoustics AD226 audiometer (Interacoustics, DK-5500, Middelfart, Denmark) with Amplivox Audiocup earphones, which have a lower test limit of -10 dB. The test sequence began with 1000 Hz, followed by 2000 Hz, 3000 Hz, 4000 Hz, 6000 Hz, 8000 Hz, 500 Hz, 250 Hz, and then a retest at 1000 Hz, after which the thresholds were recorded on the audiogram. Participants were trained and instructed on the pure tone audiometry prior to the testing. In this study, hearing loss was defined as hearing threshold\u0026thinsp;\u0026ge;\u0026thinsp;25 dB hearing loss at any of 3000, 4000, or 6000 Hz in either ear [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e].\u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eQuestionnaire Assessment\u003c/h2\u003e \u003cp\u003eTwo research assistants interviewed the workers, using a structured questionnaire. The interviews were performed at the workplace, inside the soundproof booth. Information was obtained about sociodemographic variables, including age, gender, and educational status (never been to school/primary education/secondary education/tertiary education and above). Workers were asked to report their work duration in years. They were also asked about lifestyle factors; drinking alcohol (yes/no) and current cigarette smoking (yes/no). Workers were also asked if their parents had hearing loss (yes/no), if they had experienced an ear infection the past year (yes/no), if they had high blood pressure (yes/no), if they had diabetes (yes/no) and if they had used ototoxic drugs such as quinine the past week (yes/no). Moreover, workers were asked if they experienced ringing sounds in the ears (yes/no) and if they were bothered by ringing, roaring, or buzzing in their ears or head when going to sleep (yes/no).\u003c/p\u003e \u003cp\u003eIn addition, there were questions about previous work in a noisy workplace (yes/no), and if they were living in areas with noise, for example churches, mosques, milling machines, bars, and generators (yes/no). They were also asked if they were engaged in noisy leisure time activities, including visits to discotheques, playing in a band, attending concerts, listening to music with loud volume (yes/no), and were using of ear phones to listen music or phone calls (yes/no).\u003c/p\u003e \u003cp\u003eThe original questionnaire was in English language and was translated to Kiswahili language and back to English language again. Only very minor adjustments were made in the Kiswahili version after this exercise. Pretesting of the questionnaire was performed before the main study among 20 participants from another company to assess the clarity and quality of the tool.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003eStatistical Analysis\u003c/h2\u003e \u003cp\u003eAudiometry data were entered in SPSS version 27 and Microsoft Excel. Descriptive statistics were calculated. Comparisons of groups were performed using Chi- square tests or Fischer\u0026rsquo;s exact test, depending on the expected cell count. An independent t-test was used to compare continuous variables. Due to the high prevalence of hearing loss, relative risk and 95% confidence intervals were calculated using logistic regression analysis. A correlation analysis of age and duration of work was performed by calculating the Pearson\u0026rsquo;s correlations coefficient. Significance level was set to 0.05.\u003c/p\u003e \u003cp\u003eMultivariable logistic regression analysis was used to analyze the association between hearing loss and work duration, while adjusting for other variables known to influence hearing ability including education level, previous work in a noisy workplace, living in areas that have noise apart from work, use of ear phones, engagement in leisure activities, use of ototoxic drugs the past week, current cigarette smoking and drinking alcohol. We did not include presence of chronic diseases (diabetes and high blood pressure) in the analysis, as very few workers reported such conditions.\u003c/p\u003e \u003cp\u003eThe regression analyses were performed with high-noise-exposed workers only. To control properly for age, we repeated the regression analysis including only high-noise-exposed workers below 44 years [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e\n\u003cp\u003e\u003cstrong\u003eEthical Approval\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eEthical approval (MUHAS-REC-04-2022-1082) was obtained from the Institutional Review Board (IRB) from Muhimbili University of Health and Allied Sciences (MUHAS) and by the Regional Committee for Medical and Health Research Ethics (REK) South-East Norway (No 634637/2023). All participants signed an informed consent, and all information collected in this study was kept confidential. All research was performed in accordance with relevant guidelines/regulations in Tanzania and Norway, and the research was performed in accordance with the Declaration of Helsinki.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003e\u003cstrong\u003eDescriptive characteristics of participants\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study involved only male workers (n=250). High-noise-exposed workers were older than the low-noise-exposed workers. More than two-thirds of high-noise-exposed workers (69.7%) had worked for more than six years in the small-scale metal industries, whereas the 95.8 in low-noise-exposed group had worked for less than five years. The two groups were also different in terms of their educational level, their engagement in leisure activities, daily smoking, and the use of alcohol. The two groups did not differ in previous employment in noise exposed workplaces or in their medical history, with the exception that use of ototoxic drugs within a week before the hearing test was more common among the high-noise-exposed (Table 1).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 1:\u0026nbsp;\u003c/strong\u003eDescriptive characteristics of high- and low-noise-exposed workers\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"624\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eVariable\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;High-noise exposed group\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e(n=178)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eLow-noise exposed group (n=72)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003ep-value\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eMean age in years (Standard deviation)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e34.4 (9.1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e25.6 (6.2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.001\u003csup\u003e1\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eNo (%)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eNo (%)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eAge group in years\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.001\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e18-35\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e103 (57.9)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e67 (93.1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e36-43\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e48 (27.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e3 (4.2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e44-59\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e27 (15.2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e2 (2.8)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eEducation level\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.001\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003ePrimary school and below\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e137 (77.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e25 (34.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eSecondary school and above\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e41 (23.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e47 (65.3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eDuration of work in years\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1-5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e54 (30.3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e69 (95.8)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.001\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e6 and above\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e124 (69.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e3 (4.2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003ePrevious work in noisy workplace\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e78 (43.8)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e26 (36.1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.263\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eCurrent living in areas with activities that generate noise\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e60 (33.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e12 (16.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.007\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"4\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eMedical history\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eParents with hearing loss\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e19 (10.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e8 (11.1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.920\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003ePrevious ear infection\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e21 (11.8)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e10 (13.9)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.650\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eHigh blood pressure\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e9 (5.1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1 (1.4)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.163\u003csup\u003e3\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eDiabetes mellitus\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e5 (2.8)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e3 (4.2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.418\u003csup\u003e3\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eUse of ototoxic drugs\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e9 (5.1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0 (0.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.044\u003csup\u003e3\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"4\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eLifestyle\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e*\u003c/strong\u003eEngaged in leisure activities \u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e43 (70.5)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e18 (29.5)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.02\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eUse of ear phones to listen music or phone calls\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e102 (57.3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e50 (69.4)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.075\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eCurrent cigarette smoking\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e43 (24.2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e9 (12.5)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.04\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eDrinking alcohol\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e42 (23.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e7 (9.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.01\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eSelf-reported tinnitus\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eExperience ringing sounds in the ears\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e35 (19.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e7 (9.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.057\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eBothered by ringing, roaring or buzzing in your ears or head when going to sleep\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e25 (14.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e4 (5.6)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.041\u003csup\u003e3\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003csup\u003e1\u003c/sup\u003e Independent samples \u003cem\u003et\u003c/em\u003e-test for continuous variables, \u003csup\u003e2\u003c/sup\u003eChi-square test for categorical variables, \u003csup\u003e3\u003c/sup\u003e Fisher’s exact test between high and low noise exposed workers. SD: Standard Deviation. *Leisure activities include visiting discotheques, playing in a band, attending concerts and listening to music with loud volume.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eHearing loss high- and low-noise-exposed workers\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eHigh-noise-exposed workers were 2.17 times more likely to develop hearing loss compared to the low-noise-exposed workers. Workers aged 18-35 were more likely to develop hearing loss compared to other age groups among the high noise exposed workers (Table 2).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 2:\u0026nbsp;\u003c/strong\u003eHearing loss among high-noise exposed workers and low-noise exposed workers\u0026nbsp;\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"624\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eVariable\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eHigh-noised exposed group (n=178)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eLow-noised exposed group (n=72)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eRR (95%CI) *\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eHearing loss\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e161 (90.4)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e30 (41.7)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e2.17 (1.64-2.86)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eHearing loss by age\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e18-35\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e87 (84.5)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e26 (38.8)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e2.18 (1.58-3.00)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e36-43\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e48 (100.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e2 (66.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1.50 (0.82-2.73)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e44-59\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e26 (96.3)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e2 (100.0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.96 (0.88-1.00)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eHearing loss by duration of exposure in years\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1-5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e41 (75.9)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e28 (40.6)\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1.87 (1.31-2.67)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e6 and above\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e120 (96.8)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e2 (66.7)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1.45 (0.98 -2.15)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eHearing loss by tinnitus \u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e32 (91.4)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e4 (57.1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1.60 (0.88-2.91)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u0026nbsp;Hearing loss was defined as hearing threshold ≥25 dB hearing loss at any of 3000, 4000, or 6000 Hz in either ear.\u003c/p\u003e\n\u003cp\u003e*RR (95% CI) = Relative Risk and 95 percent confidence interval.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eHearing thresholds of both ears among high-noise-exposed and low-noised-exposed workers\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe hearing mean thresholds were slightly higher (worse) in the left ear than in the right ear, with the largest significant differences at 4 kHz \u003cstrong\u003e(\u003c/strong\u003eFigure 2).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eLogistic regression analysis of hearing loss and work duration\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eUsing a multivariable logistic regression analysisamong the high-noise-exposed workers only, hearing loss was significantly associated with longer work duration in the high-noise-exposed workplaces (OR=1.22; 95% CI 1.08-1.38). The association was even stronger when adjusting for previous work in a noisy workplace, living in a noisy area, being engaged in noisy leisure activities, education level, use of ototoxic drugs, smoking, alcohol consumption, and previous ear infection (OR= 1.35; 95% CI 1.15-1.59) (Table 3).\u003c/p\u003e\n\u003cp\u003eAge and work duration were strongly correlated (Pearsons’s correlation coefficient 0.775), and an additional analysis restricted to workers younger than 44 years (n=151) was performed. The results showed a similar significant association between work duration and hearing loss (OR=1. 51; 95% CI 1.20-1.90), when adjusting for the same factors as in the first multivariable regression analysis (OR= 1.51; 95% CI 1.20 -1.90) (Table 4).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 3:\u0026nbsp;\u003c/strong\u003eMultivariable logistic regression analysis of hearing loss and work duration among high-noise-exposed workers (n=178)\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"608\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eCrude OR (CI)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\"\u003e\n \u003cp\u003e\u003cstrong\u003ep-value\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\"\u003e\n \u003cp\u003e\u003cstrong\u003eAdjusted OR (CI)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\"\u003e\n \u003cp\u003e\u003cstrong\u003ep-value\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eHearing loss\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eWork duration in years\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1.22 (1.08-1.38)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.002\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1.35 (1.15-1.59)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003ePreviously worked in a noisy workplace- No\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003ePreviously worked in a noisy workplace-Yes\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e2.76 (0.86-8.84)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.087\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e8.86 (1.73-45.48)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eLiving in areas that have noise apart from work- No\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eLiving in areas that have noise apart from work- Yes\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e4.22 (0.93-19.12)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.062\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e10.58 (1.83-61.28)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.008\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eUse of ear phones- No\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eUse of ear phones -Yes\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.93 (0.34-2.58)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.894\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1.62 (0.41-6.31)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.490\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eEngaged in leisure activities - No\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eEngaged in leisure activities -Yes\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e2.43 (0.86-6.84)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.092\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.08 (0.01-0.46)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.005\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eOtotoxic drugs - No\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eOtotoxic drugs-Yes\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.34 (0.07- 1.79)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.203\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.31 (0.03-2.87)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.300\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eCurrent cigarette smoking -No\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eCurrent cigarette smoking - Yes\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.96 (0.30-3.12)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.949\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1.60 (0.25-10.17)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.620\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eDrinking alcohol -No\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eDrinking alcohol-Yes\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.53 (0.18-1.53)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.238\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.41 (0.08-2.14)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.292\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eEducation (Primary school and below)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eEducation (Secondary school and above)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.97 (0.30-3.15)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.959\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e6.95 (1.15 - 42.10)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.035\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003ePrevious ear infection-No\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003ePrevious ear infection-Yes\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.38 (0.11-1.31)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.126\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.16 (0.02-1.21)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.076\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eOR=odds ratio; CI= 95 percent confidence interval. Hearing loss is defined as a hearing threshold ≥25 dB at any of 3, 4, or 6 kHz in either ear.\u003c/p\u003e\n\u003cp\u003e*Leisure activities include discotheque visits, playing in a band, attending concerts, or listening to music with loud volume sound.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 4:\u0026nbsp;\u003c/strong\u003eMultivariable logistic regression analysis of hearing loss and work duration among high-noise-exposed workers, age below 44 years (n=151)\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" align=\"\" width=\"608\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eCrude OR (CI)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\"\u003e\n \u003cp\u003e\u003cstrong\u003ep-value\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\"\u003e\n \u003cp\u003e\u003cstrong\u003eAdjusted OR (CI)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"bottom\"\u003e\n \u003cp\u003e\u003cstrong\u003ep-value\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eHearing loss\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eWork duration in years\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1.29 (1.10-1.52)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.002\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1.51 (1.20-1.90)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003ePreviously worked in a noisy workplace- No\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003ePreviously worked in a noisy workplace-Yes\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e3.05 (0.94-9.92)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.065\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e9.08 (1.42- 55.99)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.018\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eLiving in areas that have noise apart from work- No\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eLiving in areas that have noise apart from work- Yes\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e4.52 (0.99-20.71)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.052\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e12.92 (1.92- 86.89)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.009\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eUse of ear phones- No\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eUse of ear phones -Yes\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1.01 (0.35-2.95)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.983\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1.29 (0.29 -5.69)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.737\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eEngaged in leisure activities* - No\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eEngaged in leisure activities -Yes\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.45 (1.56-1.30)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.140\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.05 (0.01- 0.43)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.006\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eOtotoxic drugs - No\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eOtotoxic drugs-Yes\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.33 (0.60-1.77)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.194\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.16 (0.01 – 1.88)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.146\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eCurrent cigarette smoking -No\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eCurrent cigarette smoking - Yes\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.86 (0.26-2.85)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.802\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1.25 (0.18- 8.72)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.822\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eDrinking alcohol -No\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eDrinking alcohol-Yes\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.48 (0.16- 1.42)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.182\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.33 (0.06-1.94)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.221\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eEducation (Primary school and below)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003eEducation (Secondary school and above)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1.01 (0.31-3.34)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.987\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e8.38 (1.23-57.71)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e\u0026nbsp;0.031\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003ePrevious ear infection-No\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003ePrevious ear infection-Yes\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.58 (0.15 - 2.27)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.436\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.47 (0.05-4.38)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd\u003e\n \u003cp\u003e0.509\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eOR=odds ratio (OR); CI= 95 percent confidence interval. Hearing loss is defined as hearing threshold ≥25 dB at any of 3, 4, or 6 kHz.in the left ear.\u003c/p\u003e\n\u003cp\u003e*Leisure activities include discotheques visits, playing in a band, attending concerts or listening to music with loud volume sound.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eIn this study we observed a markedly higher prevalence of hearing loss (90.4%) among metal industry workers exposed to high noise levels compared to a reference group of cleaners who were exposed to low noise levels (41.7%) in Tanzania. A significant association was found between hearing loss and work duration in the metal industry.\u003c/p\u003e\n\u003cp\u003eThe prevalence of hearing loss observed in our study was similar to findings from a study conducted among forging workers in India, where 90% of workers demonstrated hearing loss [20]. Likewise, a study among metal workers in Botswana reported a prevalence of 78%, which is comparable to our findings [22].\u0026nbsp;However,\u0026nbsp;the prevalence of hearing loss in our study was higher than reported in a review study of 8 articles, which found hearing loss rates ranging from 13.8% to 59% among metal industry workers [42]. However, the noise levels were only evaluated in two of these review studies, and it is difficult to compare the results to the studies lacking this information. The differences in hearing loss might be related to differences in noise level exposure. Similarly, a study conducted among metal workers in\u0026nbsp;Ethiopia reported a prevalence of hearing loss of 30.7% [21]. In this study, the noise levels were measured but not reported clearly. The noise levels were reported to be above 85 dB, but details were not given. The noise levels might be at a lower level than in our present study. Furthermore, a prevalence of hearing loss of 47 % was reported in the steel industry in Egypt [10], but here the noise levels were not reported. In addition, a study among workers in small-scale metal industries in Nepal reported the prevalence of hearing loss to be 30.4%, but in this study the workplace noise level was below 85 dBA [18].\u003c/p\u003e\n\u003cp\u003eAnother study from Uganda, among metal fabricators in the informal sector, reported a hearing loss prevalence of 29.2 %, which is lower than observed in our current study. In that setting, the workers were exposed to noise levels ranging from 62 dBA during quieter periods to 108 dBA during peak hours. The comparatively lower prevalence of hearing loss in the Ugandan study might be attributed to lower noise levels, but also to the use of hearing protection, specifically earmuffs, which was used by 44.9% of the workers [23]. In contrast, area noise levels in our present study ranged from 89 dBA to 107 dBA, and no workers used hearing protection devices [9].\u003c/p\u003e\n\u003cp\u003eIn our present study, we found a significant association between work duration and hearing loss in the high- noise-exposed workplaces. Workers with five or more years at work in the metal industry had 1.35 times higher odds of developing hearing loss compared to those with shorter work experience. This finding aligns with a study conducted in Turkey, which reported that longer work duration was a significant predictor of hearing loss. Workers with more than five years of work experience were more likely to develop hearing loss compared to those with work experience 5 years or less [33]. Similarly, a study among metal workers in Ethiopia found that longer work duration at noisy workplaces was significantly associated with hearing loss [21].\u0026nbsp;Additional evidence also supports the association between longer work duration and increased risk of hearing impairment [34]. Furthermore, another study conducted among workers in metal fabrication workplaces indicated that hearing loss was strongly associated with more than five years of work experience, with such workers having 13.7 times higher odds of developing hearing loss [23].\u003c/p\u003e\n\u003cp\u003eThe workers in the present study were exposed to high noise levels ranging from 89 dBA to 107 dBA, and in addition, they did not use hearing protection devices [9]. This combination might be the reason why the prevalence of hearing loss is more than 90% in these workplaces. The low-noise-exposed group in this study had a much lower prevalence of hearing loss compared to the high-noise-exposed group. This is similar to a study performed among steel and iron industries where the prevalence of hearing loss was high among high-noise-exposed workers compared to low-noise-exposed workers [24].\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eBased on the noise exposure level, comparison with the reference group and control with potential confounding factors in the present study, it seems likely that high noise exposure has contributed to the high prevalence of hearing loss among the metal workers. This situation may have developed because small-scale industries in the informal sector are not registered in the Tanzania Occupational Safety and Health Authority (OSHA) services, and thus have limited occupational health and safety protections. The lack of work environment control in these industries may hinder preventive measures at these workplaces [9,43]. This is not uncommon in African countries. A review study from 2026, concludes that even though available occupational noise regulations might exist in some African nations, the regulations are not implemented. There are an enforcement challenge and lack of compliance to these regulations, especially in the informal sector [4]. \u0026nbsp;Therefore, there is a need for development of hearing conservation programs, health and safety policies, better legislations, and implementation of prevention measures in developing countries, especially for this informal sector.\u003c/p\u003e\n\u003cp\u003eA key strength of this study is the use of objective, standardized methods in data collection. Age is a well-known cause of hearing loss, but we controlled the age factor in our analyses. In the regression analysis, we did not include age due to its correlation with duration of work. Therefore, we performed an additional analysis restricting the participants to workers younger than 44 years to minimize age-related confounding. Questionnaire data were collected by two trained research assistants, and audiometric testing was performed by one qualified audiologist. Although having multiple data collectors may introduce bias, all personnel were thoroughly trained to ensure consistency. Because permanent, soundproof facilities were not available in the workplaces, audiometry was conducted in a noise-isolated area, using a mobile booth to maintain reliability and accuracy of the hearing assessments.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe study employed a cross-sectional study design and it was not blinded. The participants were aware of the study\u0026rsquo;s purpose when providing consent. Due to the design, we conducted regression analyses to examine the association between work duration among high noise exposed workers and hearing loss. The results showed a strong association between hearing loss and duration of work in high- noise-exposed environments at work. However, the work duration variable was restricted to only two categories. Other variables, such as noise from the home environment, exposure to leisure time music, were just categorized as yes or no. Such variables should be better assessed, using continuous variables in future research. \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe response rate was high, 87% in the high noise exposed group and 100% in the low noise exposed group. The statistical power was approximately 100%, indicating a high likelihood of detecting a true association and reducing the risk of Type II error, although it does not remove the likelihood source of bias.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe small-scale metal workers in this setting were all male. Therefore, only male workers were included in both the high and low-noise exposure groups. This reduced a potential gender-related confounding effect in susceptibility to hearing loss. However, this limits the generalizability of the findings to female workers and the broader population. Future studies should consider including a more a gender-balanced sample.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIn conclusion, the prevalence of hearing loss among small-scale metal workers with high noise exposure levels was high in this study compared to a low noise-exposed group. An association was found between work duration and hearing loss. The findings demonstrate a strong relationship between occupational noise exposure and hearing loss, which indicates the need of workplace intervention to reduce this problem. Small-scale metal industries should be systematically monitored and regulated to prevent occupational hearing loss among the workers. Development of prevention strategies, including hearing conservation programs, is essential. Extending regulatory oversight and preventive measures to workplaces in the informal sector may further help in protecting workers from high levels of occupational noise exposure.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors thank the administration of the Muhimbili University of Health and Allied Sciences (MUHAS), the Addis Ababa University (AAU), and the University of Bergen (UiB) for providing technical support in the development of this research work. We also appreciate the willingness of workers from the industries and cleaners from the university to participate in this study.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors contribution\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWJA was involved in conceptualization, data collection, analysis, and writing of this manuscript. IPN, GHS and SHM were involved in data collection. BEM, SHM, and IPN were involved in the conceptualization of the research. All authors contributed to data analysis, interpretation of the results, and critical revision of the manuscript. All authors have read and approved the final version of the manuscript for publication.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research work is funded by Norwegian Programme for Capacity Development in Higher Education and Research for Development via NORHED Project Safe work conditions by innovative Research and education QZA-21/0162 (North- South -South collaboration)\u003cstrong\u003e.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll data used in this study are not available, as there are restrictions from the ethical committees regarding sharing personal information. A minimal dataset is available on request. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of Interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors have no competing interests to declare in this research.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eNelson, D. I., Nelson, R. Y., Concha-Barrientos, M. \u0026amp; Fingerhut, M. The global burden of occupational noise-induced hearing loss. \u003cem\u003eAm. J. Indust Med.\u003c/em\u003e \u003cb\u003e48\u003c/b\u003e, 446\u0026ndash;458 (2005).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMasterson, E. A., Themann, C. L. \u0026amp; Calvert, G. M. Prevalence of hearing loss among noise-exposed workers within the agriculture, forestry, fishing, and hunting sector, 2003\u0026ndash;2012. \u003cem\u003eAm. J. Ind. 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Head Neck Surg.\u003c/em\u003e \u003cb\u003e46\u003c/b\u003e, 41 (2017).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHomans, N. C., Boons, J. H. C. \u0026amp; Goedegebure, A. Hearing loss prevalence in the aging population: updated population-based audiometric data from the Rotterdam study. \u003cem\u003eInt. J. Audiol.\u003c/em\u003e, 1\u0026ndash;9. (2025).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRaphela, F. S. A Systematic Review of Hearing Loss and Its Associated Factors Among Workers in the Metal Industry. \u003cem\u003eJ. Otorhinolaryngol. Hear. Balance Med.\u003c/em\u003e \u003cb\u003e6\u003c/b\u003e, 18 (2025).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMrema, E. J., Ngowi, A. V. \u0026amp; Mamuya, S. H. Status of occupational health and safety and related challenges in expanding economy of Tanzania. \u003cem\u003eAnn. Glob Health\u003c/em\u003e. \u003cb\u003e81\u003c/b\u003e, 538\u0026ndash;547 (2015).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"hearing loss, informal sector, metal industries, noise exposure, Tanzania","lastPublishedDoi":"10.21203/rs.3.rs-9265588/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9265588/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eSmall-scale metal industries may place workers at risk of hearing loss due to noise exposure levels that exceed 85dBA. This cross-sectional study assessed hearing loss among 178 male workers exposed to a mean noise level of 97.9 dBA and 72 male workers exposed to a mean noise level of 76.6 dBA. A structured questionnaire was used to obtain demographic and occupational information. Otoscopic examinations were conducted, followed by pure-tone audiometry performed inside a soundproof booth. Hearing loss was defined as a hearing threshold\u0026thinsp;\u0026ge;\u0026thinsp;25 dB 3000, 4000, or 6000 Hz in either ear. The prevalence of hearing loss was 90.4% in the high-noise exposure group and 41.7% in the low-noise exposure group. In regression analyses, work duration was significantly associated with hearing loss among workers exposed to high noise levels (OR\u0026thinsp;=\u0026thinsp;1.51; 95%CI: 1.15\u0026ndash;1.59), when adjustment for age, previous occupational noise exposure, leisure time noise, and lifestyle factors. The association was even stronger when the analysis was restricted to workers younger than 44 years (OR\u0026thinsp;=\u0026thinsp;1.51; 95%CI: 1.20\u0026ndash;1.90). These findings provide clear evidence of a strong relationship between occupational noise exposure and hearing loss. Preventive measures are urgently needed to reduce noise levels in metal industries and similar work environments.\u003c/p\u003e","manuscriptTitle":"Hearing loss among small-scale metal workers in Dar es Salaam, Tanzania","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-05-06 10:25:39","doi":"10.21203/rs.3.rs-9265588/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"editorInvitedReview","content":"","date":"2026-05-06T17:06:54+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"320747906174481256915736041207774021446","date":"2026-05-05T16:01:52+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-04-27T18:33:18+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2026-04-13T06:15:44+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-04-02T15:02:03+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-04-02T09:24:16+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2026-04-02T08:54:42+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"e8ac1a78-5071-45d9-a235-48920ae93010","owner":[],"postedDate":"May 6th, 2026","published":true,"recentEditorialEvents":[{"type":"editorInvitedReview","content":"","date":"2026-05-06T17:06:54+00:00","index":68,"fulltext":""},{"type":"reviewerAgreed","content":"320747906174481256915736041207774021446","date":"2026-05-05T16:01:52+00:00","index":66,"fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[{"id":67577202,"name":"Health sciences/Diseases"},{"id":67577203,"name":"Earth and environmental sciences/Environmental sciences"},{"id":67577204,"name":"Health sciences/Health care"},{"id":67577205,"name":"Health sciences/Health occupations"},{"id":67577206,"name":"Health sciences/Medical research"},{"id":67577207,"name":"Health sciences/Risk factors"}],"tags":[],"updatedAt":"2026-05-06T10:25:40+00:00","versionOfRecord":[],"versionCreatedAt":"2026-05-06 10:25:39","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9265588","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9265588","identity":"rs-9265588","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}