The effects of laparoscopic cholecystectomy, hysterectomy, and appendectomy on nosocomial infection risks.

The Nosocomial Infection Marker (NIM, patent pending, Cardinal Health) monitors and tracks nosocomial infection rates for hospitals and communities. Cardinal Health extracts data from client facilities on an ongoing basis using a secure, Health Insurance Portability and Accoutability Act- (HIPAA) compliant method. Data are cleaned and mapped in real time as they arrive at the Cardinal Health data center by proprietary software systems. Rare exceptions that are not electronically modeled are modeled by technical and clinical experts, processed and loaded. The new models are then used by the systems to process like data in the future. The Nosocomial Infection Marker is a computer algorithm that identifies the existence of nosocomial infections at the microbiological level. Specifically, the NIM algorithm distinguishes likely pathogens from contaminants, identifies duplicate isolates, and temporally determines hospital versus community-acquired pathogen acquisition [ 18 ]. In a multihospital study using comprehensive medical records review and gold-standard infectious disease physician discrepancy resolution, the NIM algorithm identified nosocomial infections with 86% sensitivity and 98.5% specificity hospital-wide, statistically outperforming Centers for Disease Control (CDC) case finding methods [ 18 ]. Unlike the NIM, traditional CDC case finding methods are subjectively applied with inconsistent results and are only used for certain types of infections, mostly in ICUs [ 18 , 19 ]. Like the NIM, the performance characteristics of CDC methods have only been formally evaluated in one study [ 19 ]. The Nosocomial Infection Marker (NIM) was used to identify nosocomial infections during hospitalization and post discharge. Data were extracted from the Cardinal Health (CAH) data repository for the period September 1, 2004 through December 31, 2006 from 22 hospitals in 15 states. Hospitals with matching International Statistical Classification of Diseases and Related Health Problems (ICD-9) procedure codes and more than 100 admissions with a primary ICD-9 procedure for cholecystectomy, appendectomy, or hysterectomy were eligible. These hospitals had a median number of beds of 359, with an interquartile range from 191 to 483 beds; one hospital exceeded 1,000 beds and two had fewer than 150. Mean hospital CMI was 1.56 with a standard deviation of 0.22. Admissions with primary Diagnosis Related Group (DRGs) listed in Table  1 comprised more than 95% of eligible admissions. When these admissions were restricted to adults 18 years and older for cholecystectomy and hysterectomy, and patients 2 years and older for appendectomy, 11,662 admissions were available for analysis. Table 1 DRGs included in the analysis % admissions NIM rate % laparoscopy Simple presentations (complexity = 0) 166 Appendectomy W/O complicated Principal Diag W Cc 3.16 2.71 67.21 167 Appendectomy W/O Complicated Principal Diag W/O Cc 14.53 1.12 71.66 195 Cholecystectomy W C.D.E. W Cc 0.52 14.75 16.39 196 Cholecystectomy W C.D.E. W/O Cc 0.21 0.00 25.00 197 Cholecystectomy Except By Laparoscope W/O C.D.E. W Cc 3.64 9.43 11.79 198 Cholecystectomy Except By Laparoscope W/O C.D.E. W/O Cc 2.01 2.56 40.60 358 Uterine & Adnexa Proc For Non-Malignancy W Cc 11.43 3.30 36.53 359 Uterine & Adnexa Proc For Non-Malignancy W/O Cc 25.72 1.20 47.92 493 Laparoscopic Cholecystectomy W/O C.D.E. W Cc 14.86 4.15 100 494 Laparoscopic Cholecystectomy W/O C.D.E. W/O Cc 11.42 0.68 100 Complex presentations (complexity = 1) 164 Appendectomy W Complicated Principal Diag W Cc 2.96 9.28 47.25 165 Appendectomy W Complicated Principal Diag W/O Cc 3.39 3.04 54.43 354 Uterine, Adnexa Proc For Non-Ovarian/Adnexal Malig W Cc 2.24 8.05 5.36 355 Uterine, Adnexa Proc For Non-Ovarian/Adnexal Malig W/O Cc 2.04 2.10 19.33 357 Uterine & Adnexa Proc For Ovarian Or Adnexal Malignancy 1.89 10.00 5.00 Diag = Diagnosis; W/O = Without; C.D.E. = Common Duct Exploration; Proc = Procedure; Malig = Malignancy; W = With; Cc = Complication and comorbidities DRGs included in the analysis Diag = Diagnosis; W/O = Without; C.D.E. = Common Duct Exploration; Proc = Procedure; Malig = Malignancy; W = With; Cc = Complication and comorbidities Data elements included NIMs, age, gender, insurance type (Medicaid, Medicare, private, other), hospital case mix index (CMI), primary DRG, whether or not the admission was through emergency department (ED), and ICD-9 procedure codes. The primary ICD-9 procedure code was used to identify both procedure (cholecystectomy, appendectomy, or hysterectomy) and type of approach (open or laparoscopic) and the primary DRG was used to differentiate simple from complex presentations in an attempt to account for intrinsic infection risks and biases towards open approaches. DRGs indicating malignancy or other complex presentations were assigned a complexity value of 1, as shown in Table  1 . Hospital CMI was used to control for differences between and clustering within hospitals. Single and multiple logistic regression analyses were performed to quantify the associations between NIM rate and procedure, approach, patient age, gender, insurance type, complexity of presentation, ED admission status, and hospital CMI. The first model pooled all three procedures and included binary variables to adjust for the influence of each procedure on the acquisition of NIMs. Then separate models for cholecystectomy, appendectomy, and hysterectomy were constructed. Finally models were constructed for procedure and approach for wound, urinary tract, bloodstream, and respiratory tract NIMs.

Hysterectomies comprised 43.3% of all procedures, cholecystectomies 32.7%, and appendectomies 24.0%. The percentage of cholecystectomies, appendectomies, and hysterectomies that were laparoscopic was 84.7%, 65.6%, and 39.5%, respectively. Unsurprisingly, fewer than one-quarter of all patients were male. Approximately 19.3% of admissions were covered by Medicare, 7% by Medicaid, 58.8% by private health insurance, and the remaining 14.8% by other types of insurance. NIM rates were defined as the number of admissions with at least one NIM divided by the total number of admissions. Of the 11,662 admissions, 337 (2.89%) had at least one NIM (Table  2 ). Overall, NIM rates were higher for open approaches (4.09%) than laparoscopic ones (2.11%). NIM rates were highest for cholecystectomy (3.57%), followed by appendectomy (2.60%), then hysterectomy (2.53%). Table 2 Nosocomial infection rates by approach and procedure Admissions Admissions with ≥1 NIM Rate (%) 11,662 337 2.89 Approach   Laparoscopic 7061 149 2.11   Open 4601 188 4.09 Procedure   Cholecystectomy 3808 136 3.57   Appendectomy 2803 73 2.60   Hysterectomy 5051 128 2.53 Approach by procedure   Laparoscopic     Cholecystectomy 3226 84 2.60     Appendectomy 1840 42 2.28     Hysterectomy 1995 23 1.15   Open     Cholecystectomy 582 52 8.93     Appendectomy 963 31 3.21     Hysterectomy 3056 105 3.44 Nosocomial infection rates by approach and procedure There were 399 NIMs identified in 337 admissions. Of all NIMs identified, 118 (30%) were from surgical wounds, 122 (31%) were from the urinary tract, 37 (9%) were from the blood, 29 (7%) were from the respiratory tract, and 93 (23%) were from other sources. At least one post-discharge NIM was identified in 136 admissions, accounting for 40% of all admissions with a NIM. Of the 147 post-discharge NIMs, 39% were from surgical wounds, 31% were from the urinary tract, 7% were from blood, and 22% were from other sources. Of the 136 total admissions with at least one post-discharge NIM, 92 patients had NIM-associated readmissions. Simple logistic regressions examined associations between NIM rates and surgical approaches (laparoscopic or open), and the following covariates: gender (male, female), age (<18 y, 18–34 y, 35–49 y, 50–64 y, 65–74 y, ≥75 y), surgical procedure (cholecystectomy, appendectomy, hysterectomy), type of insurance (private, Medicare, Medicaid, other), complexity of admission on presentation (0/1), admitted through ED (0/1), and hospital CMI. The results, summarized in Table  3 , show significantly higher NIM rates for males, adults aged ≥65 years, patients undergoing cholecystectomy, complex admissions, and admissions covered by Medicare; and significantly lower NIM rates for laparoscopic surgery, females, adults 18–49 years old, patients undergoing hysterectomy, and those covered by private insurance. NIM rates were positively correlated with hospital CMI, but were unaffected by ED admission status. Table 3 Univariate analyses of factors associated with NIM Variable Category NIM rate (%) OR 95% CI Gender Male 3.84 1.50 1.19–1.90 Female 2.59 Age <18 years 2.41 0.82 0.49–1.39 18–34 years 1.50 0.46 0.32–0.65 35–49 years 2.20 0.66 0.52–0.84 50–64 years 3.41 1.25 0.97–1.61 65–74 years 3.89 1.41 1.02–1.95 ≥75 years 7.10 2.96 2.25–3.90 Insurance Private 2.11 0.51 0.42–0.65 Medicare 5.24 2.32 1.85–2.92 Medicaid 3.19 1.12 0.74–1.68 Other 2.77 0.95 0.70–1.29 Approach Laparoscopic 2.11 0.32 0.21–0.52 Open 4.09 Procedure Cholecystectomy 3.57 1.41 1.13–1.76 Appendectomy 2.60 0.87 0.67–1.13 Hysterectomy 2.53 0.79 0.64–0.97 CMI 2.28 1.59–3.27 Complexity Complex 6.31 2.74 2.14–3.50 Not complex 2.40 Emergency department admission Emergent 3.03 1.06 0.72–1.55 Nonemergent 2.88 CI: confidence interval; NIM: nosocomial infection marker; OR: odds ratio Univariate analyses of factors associated with NIM CI: confidence interval; NIM: nosocomial infection marker; OR: odds ratio Since ED admission status was insignificant in the univariate analysis, it was excluded from the multivariable analyses. Pairwise correlations of all remaining covariates were performed, and all pairs were reasonably uncorrelated. Therefore, all were included in the multivariable analyses. Results of multiple logistic regression models, which controlled for gender (male, female), age (<18 yr, 18–34 yr, 35–49 yr, 50–64 yr, 65–74 yr, ≥75 yr), type of insurance (private, Medicare, Medicaid, other), complexity of admission on presentation (0/1), and hospital CMI, show that laparoscopic procedures reduced the odds of acquiring a nosocomial infections by half, but that the effect is entirely attributable to reduced infection risks in laparoscopic cholecystectomy and hysterectomy with odds ratios (ORs) of 0.34 ( p  < 0.01) and 0.48 ( p  < 0.01), respectively. No change in nosocomial infection risk was found for laparoscopic appendectomy. Estimates for individual procedures are shown in Table  4 . Table 4 Multivariable logistic regression analyses of factors associated with NIM Variable Odds ratio for NIM Pooled ( n  = 11,662) Cholecystectomy ( n  = 3,808) Appendectomy ( n  = 2,803) Hysterectomy ( n  = 5,051) Laparoscopy 0.48** 0.34** 0.97 0.48** Type of procedure     Cholecystectomy 1.87** – – –     Hysterectomy 1.05 – – – Age     <18 years 0.83 – 0.90 –     18–34 years 0.64* 0.47 0.84 0.72     50–64 years 1.22 2.13* 1.00 0.96     65–74 years 1.02* 2.21* 0.58 0.51     ≥75 years 1.92** 4.04** 3.31 0.61 Male 1.4* 1.11 1.89* – Type of insurance     Medicare 1.42 1.33 1.12 2.09*     Medicaid 1.45 3.47** 1.11 0.79     Others 1.29 1.53 1.22 1.32     CMI 1.63* 1.09 1.31 2.88*     Complexity 2.45** NS 3.95 2.54** ** Statistically significant at the 1% level * Statistically significant at the 5% level Multivariable logistic regression analyses of factors associated with NIM ** Statistically significant at the 1% level * Statistically significant at the 5% level Consistent with results of the univariate analyses, multivariable regression showed a significantly higher risk of NIMs for males, patients aged ≥65 years, and complexity of presentation at the time of admission. CMI was found to be significant in both univariate and multivariable analyses [OR = 1.63 (CI 95 1.11–2.40), p  < 0.05], and this risk was significantly higher for hysterectomy patients, for whom the odds of acquiring a NIM were as high as 2.88 times that of not acquiring NIM. Analysis of the same dataset by source of infection (urinary tract, wounds, respiratory tract, bloodstream, and others) revealed that the overall infection rates at each of these sites were all statistically significantly lower for laparoscopic approaches, as summarized in Table  5 . The odds of acquiring a site-specific infection were statistically significantly lower for all sites in laparoscopic cholecystectomy and for wound sites in hysterectomy. Table 5 Odds ratios by source Urinary tract Wound Respiratory tract Bloodstream Others Overall OR (95% CI) 0.61 (0.38–0.96) 0.41 (0.27–0.62) 0.20 (0.08–0.49) 0.31 (0.14–0.65) 0.52 (0.33–0.82) By procedure     Cholecystectomy 0.48 (0.24–0.97) 0.20 (0.11–0.39) 0.17 (0.06–0.45) 0.23 (0.10–0.55) 0.34 (0.18–0.64)     Appendectomy 0.83 (NS) 1.06 (NS) 0.27 (NS) Too few NIMs 0.91 (NS)     Hysterectomy 0.76 (NS) 0.27 (0.09–0.79) Too few NIMs 0.48 (NS) 0.62 (NS) OR: odds ratio, CI: confidence interval, NS: not significant Odds ratios by source OR: odds ratio, CI: confidence interval, NS: not significant There were no significant differences between laparoscopic versus open appendectomy for all sources of nosocomial infections (urine, blood, wound, respiratory, and other). However, laparoscopic appendectomy is associated with a statistically significantly higher risk of abscess ( p  < 0.05), a finding consistent with the literature [ 12 ]. Forty-one percent of patients with a nosocomial infection had at least one post-discharge nosocomial infection, and 58 of 115 (50%) of surgical wound infections were post discharge. There were 118 readmissions associated with at least one post-discharge NIM, and post-discharge NIMs associated with readmission were significantly lower for laparoscopic approaches ( p  < 0.001). Excluding appendectomy, the odds ratio for laparoscopic versus open NIM-associated readmission was 0.346 (CI 95 0.19–0.63).

This study demonstrates that laparoscopic cholecystectomy and hysterectomy reduced the overall odds of acquiring nosocomial infections from all sources by more than 50% and reduced the odds of readmission with nosocomial infection by two-thirds. Laparoscopic appendectomy showed no differences in overall nosocomial infection risks compared to open surgery. The findings for wound infections are consistent with results from randomized trials, which have reported statistically significantly lower surgical site infection rates for laparoscopic approaches [ 10 – 12 , 20 ]. This study also demonstrates statistically significant differences in source-based infection risks by procedure and approach. Specifically, wound, bloodstream, respiratory tract, urinary tract, and other nosocomial infections were all statistically significantly less likely to occur in association with laparoscopic cholecystectomy. Risks of wound infections in laparoscopic hysterectomy were also significantly lower than in open procedures. However, no differences in infection risks were found between laparoscopic and open appendectomy. It was important to stratify admission by complexity of presentation to avoid biases associated with complex presentations, higher intrinsic infection risks, and surgical approaches; for example, primary DRGs indicating malignancy or complex presentations (Table  1 ) were associated with open surgical approaches in 69% of admissions, whereas simple presentations were associated with open approaches in only 35% of admissions. Complex presentations are also commonly believed to be at higher risk of infections, an association that is also demonstrated in this analysis. Therefore, by controlling for presentation complexity, this analysis accounts for some of the intrinsic risk of infection as well as a bias towards open surgical approaches. The difference in patient severity between hospitals was accounted for by using CMI, and indeed CMI is significant in the univariate and multivariable models, with CMI contributing to nosocomial infection risks. Interestingly, admission through the emergency department was not significant in determining differences in nosocomial infection risks. One possible explanation is that emergency department use is a crude measure of patient severity because it may also be related to other factors such as time of day of admission and socioeconomic status. However, other variables associated with comorbidity, like age and certain payer types, were significant. While a variety of confounders were controlled for, this study is limited by the absence of certain data; for example, antibiotic use, anesthesia scores, wound class, body mass index, prior hospitalization, and certain comorbidities (i.e., cardiovascular status, diabetes mellitus, and immunodeficiency) were unavailable. These variables could explain additional NIM risk. Although omitted-variable bias is often a concern in multivariable modeling using retrospective databases, the similarity of findings in our univariate and multivariable analyses suggest that these results are robust. This study documents for the first time that laparoscopic hysterectomy and cholecystectomy are associated with statistically significantly lower overall risks of nosocomial infections ( p  < 0.01). Laparoscopic hysterectomy and cholecystectomy were also associated with statistically significantly fewer readmissions with nosocomial infections ( p  < 0.01). Differences in infection risks between laparoscopic and open appendectomy were not found to be statistically significant, suggesting that these differences are likely small or nonexistent. Where differences in risks have been demonstrated, future studies should be performed to quantify their effects on health care costs and length of stay. Other important directions for future research include controlling for potentially important confounders to test the robustness of our results and extending the analysis to examine the effect of laparoscopic versus open surgery on the risk of nosocomial infections for additional surgical procedures. Another interesting avenue for future research would be to examine the effect of hospital volume on the rate of nosocomial infections.