High SARS-CoV-2 antibody prevalence among healthcare workers exposed to COVID-19 patients

Abstract

The seroprevalence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was examined among 105 healthcare workers (HCWs) exposed to four patients who were laboratory confirmed with coronavirus disease 2019 (COVID-19), the disease caused by SARS-CoV-2 infection. These HCWs were immediately under quarantine for 14 days as soon as they were identified as close contacts. The nasopharyngeal swab samples were collected on the first and 14^th day of the quarantine, while the serum samples were obtained on the 14^th day of the quarantine. With the assay of enzyme immunoassay (EIA) and microneutralization assay, 17.14% (18/105) of HCWs were seropositive, while their swab samples were found to be SARS-CoV-2 RNA negative. Risk analysis revealed that wearing face mask could reduce the infection risk (odds ratio [OR], 0.127, 95% confidence interval [CI] 0.017, 0.968), while when exposed to COVID-19 patients, doctors might have higher risk of seroconversion (OR, 346.837, 95% CI 8.924, 13479.434), compared with HCWs exposed to colleagues as well as nurses and general service assistants who exposed to patients. Our study revealed that the serological testing is useful for the identification of asymptomatic or subclinical infection of SARS-CoV-2 among close contacts with COVID-19 patients.

Keywords: COVID-19; Healthcare workers; Risk factors; SARS-CoV-2; Seroprevalence.

Fig. 1

Detailed timeline of exposure and illness onset of the four COVID-19 patients identified in our hospital and the quarantine timeline for the 105 healthcare workers exposed as close contacts. The cycle threshold (Ct) of values of SARS-CoV-2 RNA from nasopharyngeal swab samples at hospital admission were marked.

Fig. 2

Seroprevalence analysis of SARS-CoV-2 with EIA assay and microneutralization assay. (A) The detection of IgM and IgG humoral responses against RBD and NP protein were detected by using sera samples diluted at 1:20 using EIA assay. Dashed blue line indicated cut-off value for each EIA assay, which was determined based on archived serum samples collected before COVID-19 outbreak. Sera from healthy controls (HC) collected in 2019 and the non-COVID-19 pneumonia patients were included as negative control, whereas 60 samples collected at different time points from 20 COVID-19 patients were used as positive control. Serum samples were collected on 14^th day of the quarantine from 105 HCWs and they were also tested to determine IgM and IgG responses for RBD and NP protein. (B) The correlation analysis between anti-NP IgM and OD_450nm-620nm value of anti-RBD IgM (left panel) and the correlation analysis between anti-NP IgG and OD_450nm-620nm value of anti-RBD IgG (right panel). (C) The correlation analysis between the neutralization percentage of serum and anti-NP IgG (left panel) and the correlation analysis between the neutralization percentage of serum and OD_450nm-620nm value of anti-RBD IgG (right panel). OD_450nm-620nm = optical density at 450nm-620nm. NP = nucleoprotein. RBD = receptor-binding domain.