Abstract
Background: Healthcare workers (HCWs) pose a higher risk of infection caused by SARS-CoV-2, leading to more frequent swab and testing with real-time PCR. Serology test to detect SARS-CoV-2 antibodies in the blood is easier and could be useful as part of surveillance. This study aims to determine the prevalence and incidence of infection caused by SARS-CoV-2 by serology testing in frontline HCWs. Methods: This study was prospectively conducted in 360 HCWs (240 frontline and 120 non-frontline HCWs) at Siriraj Hospital between June 2020 and April 2021. Blood samples taken at baseline, 4 weeks, 12 weeks and 48 weeks were tested for qualitative IgG using Pan-IgG [Elecsys Anti-SARS-CoV-2]) and quantitative IgG measured by anti-SARS-CoV-2 RBD IgG enzymes-linked immunoassay (ELISA). The cut-off of negative and positive control were 0.64 and 1.60, respectively. The samples positive by anti-SARS-CoV-2 RBD IgG were tested with micro-neutralizing assay (NT). Results: Among 360 HCWs, 82.2% were female and the median age was 32.5 years. One participant in non-frontline HCWs had positive rapid IgG test from baseline throughout 48 weeks but negative testing by anti-SARS-CoV-2 RBD IgG. With the cut-off determined in the study, two participants in frontline HCWs had positive anti-SARS-CoV-2 RBD IgG from baseline throughout 48 weeks and no participants had seroconversion afterward, given the prevalence of SARS-CoV-2 infection among frontline HCWs of 0.83% (2/240). One participant in non-frontline HCWs had seroconversion at 12 weeks, given the incidence of SARS-CoV-2 infection among non-frontline HCWs of 0.83% (1/120). Approximately 13-17 participants in frontline and 4-7 participants in non-frontline HCWs had borderline level of anti-SARS-CoV-2 RBD IgG. Testing with micro-NT for all samples with positive and borderline anti-SARS-CoV-2 RBD IgG showed negative result with the titers less than 1:10. Further study of the cross-reactivity with other human coronavirus is ongoing. Conclusions: The prevalence and incidence of HCWs was extremely low and no difference of infection was found between the frontline and non-frontline HCWs during the limited spread of transmission and well-control of COVID-19 outbreak. Serology testing with different methods may show the discordant result. Further study of the cross-reactivity with other human coronavirus is ongoing
