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11.11.2020 | COVID-19 | Original Article Zur Zeit gratis

Evaluating the serological status of COVID-19 patients using an indirect immunofluorescent assay, France

European Journal of Clinical Microbiology & Infectious Diseases
S. Edouard, P. Colson, C. Melenotte, F. Di Pinto, L. Thomas, B. La Scola, M. Million, H. Tissot-Dupont, P. Gautret, A. Stein, P. Brouqui, P. Parola, J.-C. Lagier, D. Raoult, Michel Drancourt
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The online version contains supplementary material available at https://​doi.​org/​10.​1007/​s10096-020-04104-2.

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An indirect in-house immunofluorescent assay was developed in order to assess the serological status of COVID-19 patients in Marseille, France. Performance of IFA was compared to a commercial ELISA IgG kit. We tested 888 RT-qPCR-confirmed COVID-19 patients (1302 serum samples) and 350 controls including 200 sera collected before the pandemic, 64 sera known to be associated with nonspecific serological interference, 36 sera from non-coronavirus pneumonia and 50 sera from patient with other common coronavirus to elicit false-positive serology. 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. IFA presented substantial agreement (86%) with ELISA EUROIMMUN SARS-CoV-2 IgG kit (Cohen’s Kappa = 0.61). The presence of antibodies was then measured at 3% before a 5-day evolution up to 47% after more than 15 days of evolution. We observed that the rates of seropositivity 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 detection anti-SARS-CoV-2 antibodies is useful as a marker associated with COVID-19 severity. The IFA assay reported here is useful for monitoring SARS-CoV-2 exposure at the individual and population levels.

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