ABSTRACT
Introduction: LTCFs are at risk of COVID-19 outbreaks but evidence regarding SARS-CoV-2 acquisition and transmission routes among their employees remains weak. Objectives: We investigated the relative contribution of occupational (vs. community) exposure for COVID-19 acquisition among employees of a university affiliated LTCF in Switzerland, from March to June 2020. Methods: This is a prospective cohort study with a nested analysis of a COVID-19 seroprevalence study among LTCF staff. We performed Poisson regression to determine risk factors for seropositivity and to measure the influence of community vs. nosocomial exposure to COVID-19 on SARS-CoV-2 seropositivity using adjusted prevalence ratios (aPR). In addition, we conducted a COVID-19 outbreak investigation in a LTCF ward using both epidemiological and genetic sequencing data. We constructed a maximum likelihood phylogenetic tree and evaluated strain relatedness to discriminate between community- vs. hospital-acquired infections among employees. Results: Among 285 LTCF employees, we included 176 participants in the seroprevalence study, of whom 30 (17%) became seropositive for SARS-CoV-2. The majority (141/176, 80%) were healthcare workers and had ≥ 1 symptom compatible with COVID-19 (127/167, 76%). Risk factors for seropositivity included exposure to a COVID- 19 patient in the LTCF (aPR 2.6;95%CI 0.9-8.1) and exposure to a SARS-CoV-2 positive person in the community (aPR 1.7;95%CI 0.8- 3.5). Among 18 employees included in the outbreak investigation, phylogenetic analysis suggests that 8 (44%) acquired their infection in the community. Conclusion: During the first pandemic wave, there was a high burden of COVID-19 among LTCF employees. Both occupational and community exposures contributed to seropositivity and infection risk. These data may allow to better assess occupational health hazards and related legal implications during the COVID-19 pandemic. (Figure Presented).