SARS-CoV-2 seroprevalence among workers in a hospital in Madrid

Background: The impact of the first wave of the pandemic due to SARS-CoV-2 has been enormous in Spanish hospitals, being Madrid one of the most affected communities. The aim of this study was to analyze the impact of the pandemic on the workers of a hospital located in one of the most affected areas of Madrid (Alcala de Henares) using a chemiluminescence immunoassay (CLIA). Methods: We conducted a seroprevalence survey between June 25th and July 31st, 2020, over hospital workers from our institution. This study population was previously analyzed using a diagnostic approach which consisted of PCR and a serologic rapid test. For the present survey, prevalence of IgG antibodies against SARS-CoV-2 was studied using chemiluminescence. We analyzed the prevalence in healthcare workers (HCW) and non-healthcare workers (nHCW). Information about professional category, use of personal protective equipment (PPEs) and previous COVID-19 contacts was collected to determine the risk factors associated with SARS-CoV-2 seropositivity. Comparisons were made using the Mann-Whitney U test (continuous variables) and the two-tailed Fisher's exact test (categorical variables). Risk factors for seropositivity were analyzed using multivariate logistic regression. Results: A total of 2,219 workers were included and 847 of them (38.2%) presented IgG antibodies against SARS-CoV-2, being seroprevalence significantly higher for HCW (39.3%) than for nHCW (30.7%, p=0.006). We found no differences regarding positivity rates compared with the first diagnostic approach for symptomatic and asymptomatic workers, or infected workers per professional category. In the multivariate logistic regression analysis, the use of PPE (protective, OR=0.65; 95%CI: 0.48-0.89; p<0.001) and previous contact with COVID-19 patients (risk factor, OR=1.93; 95%CI: 1.37-2.72; p<0.001) were independent factors that were associated with SARS-CoV-2 seropositivity. Conclusions: More than 38% of our workers presented IgG antibodies against SARS-CoV-2. We found no differences in the positivity rates between diagnostic approaches. The use of PPE (protective) and previous contact with COVID-19 patients (risk factor) were associated with infection.