Abstract
COVID-19 serological tests complement the molecular diagnostics and can be used as important tool for serosurveillance and vaccine efficiency evaluation. The aim of this study was to develop and evaluate the diagnostic performance of an in-house ELISA for retrospective serosurveillance of SARS-CoV-2. Total IgG and IgM levels in sera of PCR positive SARS-CoV-2 patients (n = 50) from North Colombo Teaching Hospital were evaluated and compared with sera (n = 50) collected from prepandemic healthy individuals as controls. Patient sample collection was initiated before vaccination programme was widely started within the country. Seropositivity of 94.0% (n = 47/50) was observed for either IgG or IgM anti-SARS-CoV-2 antibodies against receptor binding domain of spike protein or nucleocapsid protein in confirmed cases while none of controls were seropositive. In contrast, the seropositivity of only 48.0% (n = 24/50) was demonstrated with commercial ELISA kits for detection of IgG or IgM. All samples detected seropositive by commercially available kits remained seropositive with either in-house IgM or IgG ELISA. Significant correlations (p ≤ 0.001) were observed between Ab levels and day of sampling from the onset of illness. The overall sensitivity values of the in-house assays were 66.7%, 96.9%, and 100.0% for the first, second, and third week or longer after onset of symptoms for either in-house IgM or IgG ELISAs. Majority of the patients (>80.0%) were seropositive, regardless of age (<60 vs. >60 years), gender (male vs. female), or clinical severity (mild vs. moderate/severe). These data suggest that the developed in-house ELISAs can be applied to assess anti-SARS-CoV-2 antibody levels induced by either natural infections or vaccination.