SARS-CoV-2 Prevalence and Seroprevalence among Healthcare Workers in Belgian Hospitals: Baseline Results of a Prospective Cohort Study

Background Given the current SARS-CoV-2 pandemic and the occurrence of a second wave, assessing the burden of disease among health care workers (HCWs) is crucial. We aim to document the prevalence of SARS-CoV-2 and the seroprevalence of anti-SARS-CoV-2 IgG among HCWs in Belgian hospitals, and to study potential risk factors for the infection in order to guide infection prevention and control (IPC) measures in healthcare institutions. Methods We performed a cross-sectional analysis of the baseline results (April 22 - April 26) of an ongoing cohort study. All staff who were present in the hospital during the sampling period and whose profession involved contact with patients were eligible. Fourteen hospitals across Belgium and 50 HCW per hospital were randomly selected. RT-qPCR was performed to detect SARS-CoV-2 RNA on nasopharyngeal swabs, and a semi-quantitative IgG ELISA was used to detect anti-SARS-CoV-2 antibodies in sera. Individual characteristics likely to be associated with seropositivity were collected using an online questionnaire. Findings 698 participants completed the questionnaire; 80.8% were women, median age was 39.5, and 58.5% were nurses. Samples were collected on all 699 participants. The weighted anti-SARS-CoV-2 IgG seroprevalence was 7.7% (95%CI, 4.7%-12.2%), while 1.1% (95%CI, 0.4%-3.0%) of PCR results were positive. Unprotected contact with a confirmed case was the only factor associated with seropositivity (PR 2.16, 95% CI, 1.4-3.2). Interpretation Most Belgian HCW did not show evidence of SARS-CoV-2 infection by late April 2020, and unprotected contact was the most important risk factor. This confirms the importance of widespread availability of protective equipment and use of adequate IPC measures in hospital settings.