Seroprevalence of SARS-CoV-2, symptom profiles and seroneutralization during the first COVID-19 wave in a suburban area, France

Background The World Health Organisation recommends monitoring the circulation of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We aimed to estimate anti–SARS-CoV-2 total immunoglobulin (IgT) antibody seroprevalence and describe symptom profiles and in vitro seroneutralization in Nancy, France, in spring 2020. Methods Individuals were randomly sampled from electoral lists and invited with household members over 5 years old to be tested for anti–SARS-CoV-2 (IgT, i.e. IgA/IgG/IgM) antibodies by ELISA (Bio-rad). Serum samples were classified according to seroneutralization activity >50% (NT50) on Vero CCL-81 cells. Age- and sex-adjusted seroprevalence was estimated. Subgroups were compared by chi-square or Fisher exact test and logistic regression. Results Among 2006 individuals, 43 were SARS-CoV-2–positive; the raw seroprevalence was 2.1% (95% confidence interval 1.5 to 2.9), with adjusted metropolitan and national standardized seroprevalence 2.5% (1.8 to 3.3) and 2.3% (1.7 to 3.1). Seroprevalence was highest for 20-to 34-year-old participants (4.7% [2.3 to 8.4]), within than out of socially deprived area (2.5% vs 1%, P= 0.02) and with than without intra-family infection (p<10 −6 ). Moreover, 25% (23 to 27) of participants presented at least one COVID-19 symptom associated with SARS-CoV-2 positivity (p<10 −13 ), with anosmia or ageusia highly discriminant (odds ratio 27.8 [13.9 to 54.5]), associated with dyspnea and fever. Among the SARS-CoV-2-positives, 16.3% (6.8 to 30.7) were asymptomatic. For 31 of these individuals, positive seroneutralization was demonstrated in vitro . Conclusions In this population of very low anti-SARS-CoV-2 antibody seroprevalence, a beneficial effect of the lockdown can be assumed, with frequent SARS-CoV-2 seroneutralization among IgT-positive patients. Key Messages Total immunoglobulin antibody (IgT) measurement is an accurate tool to monitor the circulation of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and a key biological feature to assume the spread of COVID-19 later after the appearance of symptoms. IgT seroprevalence was 2.1% in the Grand Nancy Metropolitan area, France; was highest for young adults; in socially deprived area, but this was not confirmed at the individual level; and was associated with high intra-family viral transmission. About two thirds of IgT-positive individuals exhibited SARS-CoV-2–positive seroneutralization. Trial registration NCT04448769