Antibody response using six different serological assays in a completely PCR-tested community after a COVID-19 outbreak - The CoNAN study

2020 
Abstract Objectives Due to a substantial proportion of asymptomatic and mild courses, many SARS-CoV-2 infections remain unreported. Therefore, assessment of seroprevalence may detect the real burden of disease. We aimed at determining and characterizing the rate of SARS-CoV-2 infections and the resulting seroprevalence in a defined population. The primary objective of the study was to assess SARS-CoV-2 antibody seroprevalence using six different IgG detecting immunoassays. Secondary objectives of the study were: i.) to determine potential risk factors for symptomatic vs. asymptomatic Covid19 courses; ii.) to investigate the rate of virus RNA-persistence. Methods CoNAN is a population-based cohort study performed in the community Neustadt am Rennsteig, Germany that was quarantined from March 22nd to April 5th after six SARS-CoV-2 cases were detected in the villages' population. The SARS-CoV-2 outbreak compromised 51 cases and 3 deaths. The CoNAN study was performed from May 13th to May 22nd 2020 six weeks after a SARS-CoV-2 outbreak. Results We enrolled a total of 626 participants (71% of the community population) for PCR- and antibody testing in the study. All actual SARS-CoV-2 PCR tests were negative. Fifty-two out of 620 (8.4%) participants had antibodies against SARS-CoV-2 in at least two different assays. There were 38 participants with previously PCR-confirmed SARS-CoV-2 infection. Of those, only 19 (50%) displayed anti-SARS-CoV-2 antibodies. We also show that antibody positive participants with symptoms compatible with a respiratory tract infection had significantly higher antibody levels then asymptomatic participants (EU-assay: Median 2.9 vs. 7.2 IgG-index, p=0.002; DS-assay: Median 45.2 vs. 143 AU/mL, p=0.002). Persisting viral replication was not detected. Conclusions Our data question the relevance and reliability of IgG antibody testing to detect past SARS-CoV-2 infections six weeks after an outbreak. We conclude that assessing immunity for SARS-CoV-2 infection should not only rely on antibody tests.
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