SARS-COV-2 seroprevalence among all healthcare workers in a tertiary hospital in Spain.

Background Healthcare workers (HCWs) have been a critical and vulnerable population during SARS-CoV-2 pandemic. The aim of this study was to determine the overall seroprevalence and to evaluate occupational risk factors among HCWs in one of the countries most affected by this pandemic. Methods We conducted a seroprevalence study for SARS-CoV-2 in a tertiary hospital in Madrid (Spain) between 24 April and 8 May 2020. A total of 4894 HCWs were invited for serologic testing. Serum samples were tested for SARS-CoV-2 IgM and IgG antibodies using Enzyme Immunoassay (ELISA) and Electro-Chemiluminescence Immunoassay (ECLIA) techniques. We calculated odds ratios to assess association between demographic and occupational characteristics with SARS-CoV-2 seroconversion. Results We processed 4324 serum samples. Overall, seroprevalence was of 16.6% (95% CI: 15.5-17.7). We found statistically significant differences in SARS-CoV-2 seroprevalence by type of employee, professional category, department and type of activity performed during the pandemic period, while no differences were identified between the personnel working in the COVID-19 wards compared to those working in non-COVID-19 wards. We confirmed 268 (26.7%) infections among 1005 hospital staff members tested by PCR. 60.5% of HCWs infected by SARS-CoV-2, assessed either by PCR or serology, could be considered asymptomatic or paucisymptomatic. Conclusions HCWs have an increased risk of SARS-CoV-2 infection but COVID-19 patient exposure was not a determining factor. Universal mask wearing should be mandatory in healthcare settings given the important number of asymptomatic and paucisymptomatic cases.