Prevalence of SARS-CoV-2 antibodies in hospital employees, Central Germany

Objectives Unidentified SARS-CoV-2 infections among hospital staff can become a major burden for healthcare systems worldwide. We hypothesized that the number of previous SARS-CoV-2 infections among hospital employees is substantially higher than known on the basis of direct testing strategies. A serological study was thus performed among staff of Marburg University Hospital, Germany, in May and June 2020. Methods Anti-SARS-CoV-2 antibody titers were measured by spike protein (S1)-specific IgG ELISA (Euroimmun) and by nucleoprotein-(NCP) specific total antibody CLIA (Roche). Selected sera were analyzed by SARS-CoV-2 neutralization test. Participants provided questionnaires regarding occupational, medical, and clinical items. Data for 3,623 individuals (74.7% of all employees) were collected. Results Individuals reactive to both S1 and NCP were defined as seropositive; all of those were confirmed by neutralization test (n=13). Eighty-nine samples were reactive in only one assay, and 3,521 were seronegative. The seroprevalence among hospital employees at Marburg University Hospital was 0.36% (13/3,623). Only five of the 13 seropositive employees had reported a positive SARS-CoV-2 RT-PCR test result. Conclusions Usage of a single S1-specific assay highly overestimated seroprevalence. The data provided no evidence for an increased risk for a SARS-CoV-2 infection for staff involved in patient care compared to staff not involved in patient care.