Prevalence of SARS-CoV-2 antibodies in healthy blood donors from the state of Tyrol, Austria, in summer 2020

Background Seroepidemiological studies provide important insight into the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in our society. We aimed to determine seropositivity of SARS-CoV-2 antibodies and its cross-sectional correlates in a large cohort of blood donors. Methods In this observational cohort study, we tested healthy blood donors residing in Tyrol, Austria, for SARS-CoV-2 antibodies using the Abbott SARS-CoV-2 IgG chemiluminescent microparticle immunoassay. We estimated 95% confidence intervals (95% CI) of seroprevalences using bootstrapping and tested for differences by participant characteristics using logistic regression. Findings Between 8 June and 4 September 2020, we screened 5345 healthy individuals at local blood donor sessions (mean age 42.7 years, SD 13.5 years, 46.7% female). Overall seroprevalence was 3.1% (95% CI 2.7-3.6%, 165 cases), which is 5.1-fold higher (95% CI 4.5-6.0%) than the case number identified by the health authorities in the state-wide testing program (0.6%; 4536 out of 757,634). Seroprevalence was higher in the district Landeck (16.6%, P < 0.001) and in individuals aged < 25 years (4.7%, P = 0.043), but did not differ by gender, blood types, or medication intake. The odds ratio for seropositivity was 2.51 for participants who had travelled to Ischgl (1.49-4.21, P = 0.001), 1.39 who had travelled to other federal states (1.00-1.93, P = 0.052), and 2.41 who had travelled abroad (1.61-3.63, P < 0.001). Compared to participants who had a suspected/confirmed SARS-CoV-2 infection but were seronegative, seropositive participants more frequently reported loss of smell (odds ratio = 2.49, 1.32-4.68, P = 0.005) and taste (odds ratio = 2.76, 1.54-4.92, P = 0.001). Conclusion In summer 2020, SARS-CoV-2 seroprevalence in Tyrolean blood donors was 3.1%. Our study revealed regional variation and associations with young age, travel history and specific symptoms.