High seroprevalence of SARS-CoV-2 antibodies in healthcare workers in COVID-19 wards indicates an occupational hazard-a prospective cohort study during the first year of the COVID-19 pandemic in Kalmar County, Sweden.

The aim of this study is to report the seroprevalence of SARS-CoV-2 antibodies in healthcare workers with various risk of occupational exposure in Kalmar County, Sweden, during the first year of the coronavirus disease 2019 (COVID-19) pandemic. We performed SARS-CoV-2 antibody measurements at four time points, from May 2020 to May 2021, in 401 healthcare workers (HCW) at seven hospital wards and two residential care facilities, with different risk of SARS-CoV-2 exposure. Overall, the prevalence of SARS-CoV-2 antibodies in HCW in Kalmar County was high compared to similar studies from other countries and increased from May 2020 to May 2021. Initially, 14% of the participants were SARS-CoV-2 seropositive. This number increased to 18% in September and 21% in December 2020. In May 2021, the prevalence of antibodies to nucleocapsid antigen had increased to 28%, while antibodies to spike protein had increased to 95% due to vaccination. A large variation in seroprevalence between different wards was detected and HCW in a COVID-19 designated ward had significantly higher seroprevalence than HCW working in wards without COVID-19 patients, with a risk ratio of 7.28, (95% CI 2.38-22.33) in May 2020. Our findings suggest a relationship between occupational COVID-19 exposure and seropositivity which implies that efficient hygiene routines for health- and social care workers are essential to avoid that COVID-19 care will constitute an occupational hazard.