Dynamics of humoral response to coronavirus antigens among employees of COVID-dedicated hospital: an observational study.

INTRODUCTION: During the COVID­19 pandemic studies on workplace safety of hospital staff taking care of patients with this disease are a high priority. We decided to analyze the results of opportunistic screening for anti-SARS­CoV-2 antibodies among employees of a designated COVID-19 center. OBJECTIVES: The aim of the study was to investigate whether potential exposition to SARS­CoV-2 antigens is reflected in the results of serological studies. PATIENTS AND METHODS: Every employee who performed at least a single test between April 21 and July 20, 2020 was included in the study. The tests assessed the levels of immunoglobulin (Ig) G and IgM+IgA. Employees working in direct contact with COVID­19 patients and those participating in aerosol­generating procedures were identified. RESULTS: The results of 2455 tests taken by 1572 employees were analyzed. A total of 357 participants (22.7%) had at least 1 positive or equivocal result during the study period. Linear mixed models revealed gradual increases in mean levels of both IgG and IgM+IgA antibodies among employees with all negative results. The rate of change was higher among persons who had direct contact with COVID­19 patients and the highest rate of change was observed among individuals participating in aerosol­generating procedures. CONCLUSIONS: We detected developing humoral immune response to a new set of coronavirus antigens among the study group. It is possible that employees of designated COVID­19 centers are regularly exposed to noninfectious doses of SARS­CoV-2 or its antigens.