Effectiveness of prevention of SARS-CoV-2 transmission among unvaccinated Italian healthcare workers: a nested case-control study

Background: This study aims at investigating the association between personal protection equipment (PPE) use and SARS-CoV-2 infection among healthcare workers (HCWs) during the first wave of the COVID-19 pandemic. Methods: We analyzed occupational surveillance contact forms notified between March and September 2020 by Italian HCWs, which were followed by a PCR test. The odds ratios (ORs) and 95% confidence intervals (CIs) for positive PCR test based on characteristics of HCWs and contacts, including self-reported symptoms and PPE use, were calculated through multivariable logistic regression models. Results: Overall, 4,883 contacts reported by 2,952 HCWs, were included in the analysis. A total of 224 contacts (4.6%) among 144 HCWs (4.9%) resulted in a positive PCR test. No difference was found based on sex, age, employment in a COVID-19 unit, or job title, except for an OR of 0.30 (95% CI 0.11-0.78) for resident physicians, compared to administrative staff. The ORs for use of surgical mask were 0.59 (95% CI=0.40-0.86) for use only by HCW, 0.49 (95% CI=0.22-1.07) for use only by the infected person, and 0.40 (95% CI=0.27-0.60) for use by both, compared to use by neither. Use of other PPEs was not associated with infection, while the OR for hand sanitation was 0.61 (95% CI=0.40-0.93). HCW reporting fever, cough, and asthenia had a higher risk of infection. Conclusions: Use of surgical masks was associated with a 40-60% lower risk of infection, especially when both HCW and the infected individual used it. Our results quantify the role played by mask use and hand sanitation in preventing SARS-CoVARSV-2 transmission in high-risk circumstances in the hospital setting.