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.
Keywords: COVID-19; SARS-CoV-2; healthcare worker; infection prevention and control; risk factors; seroprevalence.