Seroprevalence of COVID-19 among healthcare workers in Hong Kong: a longitudinal cohort study

Abstract

Background: Hong Kong hasinvested heavily in hospital infection control and pandemic preparedness after the severe acute respiratory syndrome (SARS) epidemic in 2003. However, healthcare workers remain a high-risk group for emerging infectious diseases due to occupational exposure to patients and potentially contaminated environments. This study aims to estimate the cumulative incidence or seroprevalence of COVID-19 among healthcare workers, who are at elevated risk of contracting the disease due to occupational exposures to patients. Methods: We conducted a longitudinal cohort study of 761 healthcare workers with varying exposures to COVID19 patients and collected blood samples between June and October 2020 to estimate the cumulative incidence or seroprevalence of COVID-19 in HCWs in Hong Kong. Seroprevalence was defined as the proportion of blood samples that were positive for antibodies against the SARS-CoV-2 virus measured by the plaque reduction neutralization test (PRNT). Results: The median age of our cohort was 34 years (range: 21, 65), and 35% were male. Most HCWs in our study worked in public hospitals and clinics, and more than half of them worked in clinical departments. Almost all (751) participants in our cohort reported at least occasional contact with patients or potentially contaminated areas in the workplace. Despite heavy exposure to the SARS-CoV-2 virus, only 18 (2.4%) serum samples were positive by enzyme-linked immunosorbent assay (ELISA) and none of the blood samples were seropositive for antibodies to the SARS-CoV-2 virus by plaque reduction neutralization assay (PRNT). This translates into an estimated seroprevalence of 0% (95% CI: 0%, 0.5%) for the first 10 months of the pandemic. Conclusions: Despite the significant community spread of COVID-19 in Hong Kong, seroprevalence among healthcare workers in Hong Kong is low. Our findings support the effectiveness of infection control precautions in healthcare workers locally.