Factors associated with SARS-CoV-2 infection among healthcare workers: a European multicentre cohort study, May 2021-April 2024

Background: Healthcare workers (HCWs) faced increased SARS-CoV-2 infection risk. We aimed to identify factors associated with SARS-CoV-2 infection in HCWs and assess how their association with infection changed over time to prepare for future similar events. Methods: We conducted a cohort study among HCWs from 18 European hospitals that completed weekly questionnaires and tested weekly/fortnightly by PCR. We defined separate cohorts for pre-Omicron (May 2021-December 2021), pandemic Omicron (December 2021-April 2023), and post-pandemic Omicron (September 2023-April 2024) periods. Using Cox proportional hazards models, we estimated adjusted hazard ratios (aHRs) for associations between each exposure and SARS-CoV-2 infection, adjusting for age, sex, underlying conditions, and hospital. Results: We included 1395, 2056, and 1254 HCWs in the three periods. Median age was 44 years, and 2597 (80%) were female, 740 (22%) medical doctors, 1399 (42%) nurses, 391 (12%) administrative personnel, 113 (3%) ancillary personnel, and 612 (18%) worked in other roles. Compared to medical doctors, ancillary personnel presented the highest risk pre-Omicron (aHR 3.86, 95% CI [1.30, 11.47]). Household contact was the strongest risk factor pre-Omicron (aHR 4.05 95% CI [1.78, 9.19]) but decreased over time. Conclusions: Household exposure and occupational role were key risk factors, but their effect size decreased over time. Infection prevention strategies should be regularly updated, extending beyond clinical staff and considering household exposure, should similar events occur. Clinical trial number: Not applicable.