Prevalence of SARS-CoV-2 IgG/IgM antibodies among Danish and Swedish Falck emergency and non-emergency healthcare workers

Background Knowledge about the COVID-19 outbreak is still sparse especially in a cross-national setting. COVID-19 is caused by a SARS-CoV-2 infection. The aim of the study is to contribute to the surveillance of the pandemic by bringing new knowledge about SARS-CoV-2 seropositivity among healthcare workers and evaluating whether certain job functions is associated with a higher risk of being infected, and to clarify if such association is mediated by the number of individuals that the employees meet during a workday. Finally, we will investigate regional and national differences in seroprevalence. Methods A bi-national prospective observational cohort study including 3,272 adults employed at Falck in Sweden and Denmark. Participants were tested for SARS-CoV-2 antibodies every second week for a period of 8 weeks from June 22, 2020 until August 10, 2020. Descriptive statistics as well as multivariable logistic regression analyses were applied. Results Of the 3,272 Falck employees participating in this study, 159 (4.9%) tested positive for SARS-CoV-2 antibodies. The seroprevalence was lower among Danish Falck employees than among those from Sweden (2.8% in Denmark and 8.3% in Sweden). We also found that number of customer or patient contacts during a workday was the most prominent predictor for seropositivity, and that ambulance staff was the most vulnerable staff group. Conclusions Our study presents geographical variations in seroprevalence within the Falck organization and shows evidence that social interaction is one of the biggest risk factors for getting infected with SARS-CoV-2. Key points SARS-CoV-2 seroprevalence vary between Denmark and Sweden, between job types and is mostly affected by number of social interactions among Falck healthcare workers