Blood samples were collected at the CHU Saint-Pierre, and the sera were tested for SARS-CoV-2-specific immunoglobulin G (IgG) using the Euroimmun Anti-SARS-CoV-2 ELISA IgG (Euroimmun, Luebeck, Germany) according to the manufacturer’s instructions for the enzyme-linked immunosorbent assay (ELISA) automated system ETI-MAX 3000 (DiaSorin, Saluggia, Italy). The Euroimmun Anti-SARS-CoV-2 ELISA IgG uses microplate wells that are coated with the SARS-CoV-2 recombinant S1 structural protein, and the results are evaluated semi-quantitatively by calculation of a ratio of the extinction of samples over the extinction of the calibrator. This test demonstrated excellent sensitivity and specificity for detection of IgG antibodies from samples collected after COVID-19 diagnosis by polymerase chain reaction (PCR) [14 (link)]. The ratio interpretation was as follows: < 0.8: negative, ≥ 0.8 to < 1.1 borderline, ≥ 1.1 = positive.
Each enrolment included a questionnaire on age, sex, medical background, contact with PCR-positive individuals, place of work, school, and kindergarten frequentation. Symptoms compatible with COVID-19 since March 2020 and up to 15 days before the serological test were also recorded. Each participant was contacted by phone to be informed of their results and eventually complete any missing information. A retrospective review of medical files was also made when necessary.
Each enrolment included a questionnaire on age, sex, medical background, contact with PCR-positive individuals, place of work, school, and kindergarten frequentation. Symptoms compatible with COVID-19 since March 2020 and up to 15 days before the serological test were also recorded. Each participant was contacted by phone to be informed of their results and eventually complete any missing information. A retrospective review of medical files was also made when necessary.
