Seroprevalence of anti-SARS-CoV-2 of IgG antibody by ELISA: Community-based, cross-sectional study from urban area of Malegaon, Maharashtra

BACKGROUND: Given the high incidence of asymptomatic or subclinical SARS-CoV-2 infection, reported cases likely underestimate the overall prevalence and infectivity of COVID-19. Serological test for IgG can provide a better measure of disease activity by identifying asymptomatic or subclinical infection. This study was conducted to estimate the seroprevalence of SARS-CoV-2 infection and to the determinants of SARS-CoV-2 infection in the hotspot area of COVID-19. METHOD: It was a community-based, cross-sectional study using multistage sampling with a sample size of 360. After informed consent, the demographic information, past history of SARI/ILI, contact, COVID-19 status were collected. The blood samples were taken from one family member for anti-SARS-CoV-2 IgG antibody by ELISA testing kit. RESULTS: Majority of the study subjects had no history of SARI (86%) or any contact with COVID-19 case (98%). Overall seroprevalence of anti-SARS-CoV-2 of IgG antibody was 40% (95% CI 35–45%), infection fatality rate (IFR) was 0.7%. Seroprevalence varied significantly depending on religious background; with Muslims (53%) seroprevalence compared to other religious groups. Seroprevalence of homemaker/unemployed (49%) and laborer (55%) was significantly higher compared to business (30%) and service occupation (21%). Subjects with overcrowding conditions and poor ventilation was significantly associated with higher seroprevalence with odds ratio of 2.5 and 2.3, respectively. CONCLUSION: The antibody testing detects a large number of asymptomatic cases or previously infected cases which would have been missed by clinical history. Thus, the number of undiagnosed cases was found significantly higher even with rigorous implementation of lockdown.