The main method by which SARS-CoV-2 is currently tested for is using qPCR-based techniques, which identifies the viral nucleic acids when they are present in sufficient quantity. However, false negative results can occur, leading to a failure to quarantine the infected patient. The authors examined the time kinetics of the various antibodies produced against SARS-CoV-2 to assess their potential for testing. The humoral response against SARS-CoV-2 included IgA, IgM and IgG responses; these were examined in 208 plasma samples from 82 confirmed and 58 probable cases. The median duration of IgM and IgA antibody detection were 5 days, while IgG was detected on day 14 following symptom onset; with a positive rate of 85.4%, 92.7% and 77.9%, respectively. In confirmed and probable cases, the positive IgM rates were 75.6% and 93.1%, respectively. The detection efficiency of IgM ELISA was found to be higher than for qPCR 5.5 days following symptom onset. The positive detection rate is significantly increased (98.6%) when the IgM ELISA assay is combined with PCR for each patient, compared with a single qPCR test (51.9%). Therefore the humoral response to SARS-CoV-2 can aid in the diagnosis of COVID-19.
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