SARS-CoV-2 seroprevalence in asymptomatic or mild symptomatic people and symptomatic patients with negative PCR results: The hidden perspective in epidemiological reports

BackgroundSARS-CoV-2 has led to the current pandemic of respiratory disease. The reports of confirmed COVID-19 cases based on molecular tests do not completely cover the total number of infected people. These reports do not include the asymptomatic or mildly symptomatic patients and also the patients with false-negative RT-PCR results, while the infection is contagious in all of these conditions. ObjectiveIn this study, we tried to improve our conception of the hidden perspective of SARS-CoV-2 in epidemiological reports. MethodsFrom May 30 to June 17, 2020, blood samples were collected from two groups of people: asymptomatic or mild symptomatic volunteer participants and severe symptomatic hospitalized patients with negative PCR results. Detection of SARS-CoV-2 antibody was done with ELISA kit targeting N or S proteins. ResultsTotally 716 samples from volunteer participants and 81 samples from symptomatic hospitalized patients with negative PCR were evaluated. The test performance-adjusted seroprevalence (95% CI) of SARS-CoV-2 anti-N IgG was 17.3% (8.8%, 25.8%) for volunteers and 25.5% (12.8%, 39.7%) for anti-N and S IgM in hospitalized group. There was an association between high-risk occupations, high-risk behaviors, or symptomatic diseases with positive SARA-Cov-2 N antibody results. Among anti-N positive infected individuals, 49.2% (21.4%, 78.8%) were anti-S positive. ConclusionThe results showed that SARS-COV-2 infection occurs in asymptomatic or mildly symptomatic individuals, but in more than half of them, the produced antibody is not protective. Findings of hospitalized patients also showed that the combination of IgM assay with real-time PCR improves the detection of the disease by more than 25% in negative molecular cases.