Post-outbreak serological screening for SARS-CoV-2 infection in healthcare workers at a Swedish University Hospital

BACKGROUND: Nosocomial outbreaks of coronavirus disease 2019 (COVID-19) can have devastating consequences from both a resource cost and patient healthcare perspective. Relying on reverse transcription-polymerase chain reaction (RT-PCR) for identifying infected individuals may result in missed cases. Screening for antibodies after an outbreak can help to find missed cases and better illuminate routes of transmission.

METHODS: In this study, we present the results of a serological screening of the healthcare workers (HCWs) on a ward for infectious diseases in Sweden with a point-of-care antibody test 8 weeks after an outbreak of COVID-19. In all, 107/123 (87%) of HCWs who were tested with RT-PCR in the outbreak investigation participated in this study on seroprevalence. Participants were also asked to fill out a questionnaire entailing epidemiological data. The cohort was stratified by RT-PCR result and the resulting groups were compared to each other.

RESULTS: Six (8%) HCWs who were tested RT-PCR negative during the outbreak investigation had developed specific IgG antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). These HCWs had all worked shifts with colleagues who later were tested RT-PCR positive during the outbreak.

CONCLUSIONS: Our results indicate that a serological follow-up screening after an outbreak may be used as a complement to virus detection in an outbreak situation. However, immunoglobulin (Ig) G-detection should also be performed at the start of an outbreak, to facilitate interpretation of the results.