Version 2 du 24 septembre 2020

Evaluating the serological status of COVID-19 patients using an indirect immunofluorescent assay, France
S. Edouard, P. Colson, C. Melenotte, F. De Pinto, L. Thomas, B. La Scola, M. Million, H. Tissot-Dupont, P. Gautret, A. Stein, P. Brouqui, P. Parola, J-C Lagier, D. Raoult, M. Drancourt

An indirect immunofluorescent assay was developed in order to assess the serological status of 888 RT-PCR-confirmed COVID-19 patients (1,302 serum samples) and controls in Marseille, France. Incorporating an inactivated clinical SARS CoV-2 isolate as the antigen, the specificity of the assay was measured as 100% for IgA titre ≥ 1:200; 98.6% for IgM titre ≥ 1:200; and 96.3% for IgG titre ≥ 1:100 after testing a series of negative controls as well as 350 serums collected from patients with non-SARS-CoV-2 Coronavirus infection, non-Coronavirus pneumonia and infections known to elicit false-positive serology. IFA presented substantial agreement (86%) with ELISA EUROIMMUN SARS-CoV-2 IgG kit (Cohen’s Kappa=0.61). Seroprevalence was then measured at 3% before a five-day evolution up to 47% after more than 15 days of evolution. We observed that the seroprevalence as well as the titre of specific antibodies were both significantly higher in patients with a poor clinical outcome than in patients with a favourable evolution. These data, which have to be integrated into the ongoing understanding of the immunological phase of the infection, suggest that serotherapy may not be a therapeutic option in patients with severe COVID-19 infection. The IFA assay reported here is useful for monitoring SARS-CoV-2 exposure at the individual and population levels.

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Figures 1-2-3-4-S1
Tables 1 et 2

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