To assess IgGs against SARS-CoV-2, we first qualitatively screened total antibodies with a chemiluminescent immunoassay, the Atellica® IM SARS-CoV-2 Total assay, using an Atellica® IM Analyzer (Siemens Healthcare, Erlangen, Germany). This assay is directed toward the receptor-binding domain (RBD) in the S1 subunit of the SARS-CoV spike (S) protein. All positive samples were re-tested with a confirmatory ELISA assay, SARS-CoV-2 (Euroimmun, Lübeck, Germany) already in use at our center for diagnostic routines. This assay provides semiquantitative in vitro determination of immunoglobulins classes IgG, using the S1 domain of the Spike protein, including RBD. Sensitivity and specificity for Atellica® IM SARS-CoV-2 Total assays were both 95% and for SARS-CoV-2 Euroimmun ELISA they were 90.3% and 98.5%, respectively. All plasma samples that were confirmed positive for SARS-CoV-2 IgG using the Euroimmunn ELISA test were considered ‘truly’ positive. Based on the random selection design, testing samples from the same subject at different times (months) were considered in the study.
We estimated an overall seroprevalence and an additional month-by-month seroprevalence as the number of ‘truly’ positive tests/total patients. Seroprevalence was reported as rate and 95% confidence intervals (CI).
We estimated an overall seroprevalence and an additional month-by-month seroprevalence as the number of ‘truly’ positive tests/total patients. Seroprevalence was reported as rate and 95% confidence intervals (CI).