Seroprevalence of SARS-CoV-2 IgG antibodies, in Corsica (France), April and June 2020.

Our aim was to assess the seroprevalence of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection after the lockdown in a sample of the Corsican population. Between 16th April and 15th June 2020, 2,312 residual sera were collected from patients having carried out a blood analysis in one of the participating laboratories. Residual sera obtained from persons of all ages were tested for the presence of anti-SARS-CoV-2 IgG using the EUROIMMUN enzyme immunoassay kit for semiquantitative detection of IgG antibodies against S1 domain of viral spike protein (ELISA-S). Borderline and positive samples in ELISA-S were also tested with an in-house virus neutralization test (VNT). Prevalence values were adjusted for sex and age. A total of 1,973 residual sera samples were included in the study. The overall seroprevalence based on ELISA-S was 5.27% [95% confidence interval (CI) 4.33-6.35] and 5.46% [4.51-6.57] after adjustment. Gender was not associated with IgG detection. However, significant differences were observed between age groups (p-value = 1 E-5) and particularly for people being younger than 50 years of age (Odd ratio (OR) = 2.86 95% CI [1.80- 4.53]; p-value <0.000001*). The prevalence of neutralizing antibody titers [≥]40 was of 3% [2.28-3.84]. In conclusion the present study showed that a low seroprevalence for COVID-19 in Corsica in accordance with values reported for other French regions in which the impact of the pandemic was low.