Prevalence and determinants of serum antibodies to SARS-CoV-2 in the general population of the Gardena Valley

Melotti, R.; Scaggiante, F.; Falciani, M.; Weichenberger, C. X.; Foco, L.; Lombardo, S.; De Grandi, A.; von Laer, D.; Mahlknecht, A.; Pramstaller, P. P.; Pagani, E.; Meier, H.; Gaertner, T.; Troi, C.; Mascalzoni, D.; Pattaro, C.; Mian, M.

Background. Community-based studies are essential to quantify the spread of SARS-CoV-2 infection and for unbiased characterization of its determinants and outcomes. We conducted a cross-sectional study in the Gardena valley, a major Alpine touristic destination which was struck in the expansion phase of the COVID-19 pandemic over the winter 2020. Methods. We surveyed 2244 representative study participants who underwent swab and serum antibody tests. We made multiple comparisons among the Abbott and Diasorin bioassays and serum neutralization titers. Seroprevalence accounted for the stratified design, non-response and test accuracy. Determinants and symptoms predictive of infection were analyzed by weighted multiple logistic regression. Results. SARS-CoV-2 seroprevalence was 26.9% (95% confidence interval: 25.2%, 28.6%) by June 2020. The serum antibody bioassays had modest agreement with each other. Receiver operating characteristic curve analysis on the serum neutralizing capacity showed better performance of the Abbott test at lower than the canonical threshold. Socio-demographic characteristics showed no clear evidence of association with seropositivity, which was instead associated with place of residence and economic activity. Loss of taste or smell, fever, difficulty in breathing, pain in the limbs, and weakness were the most predictive symptoms of positive antibody test results. Fever and weakness associations were age-dependent. Conclusion. The Gardena valley had one of the highest SARS-CoV-2 infection prevalence in Europe. The age-dependent risk associated with COVID-19 related symptoms implies targeted strategies for screening and prophylaxis planning.