High SARS-CoV-2 Seroprevalence in Children and Adults in the Austrian Ski Resort Ischgl

Abstract

Abstract Background Early March 2020, a SARS-CoV-2 outbreak in the ski resort Ischgl in Austria initiated the spread of SARS-CoV-2 throughout Austria and Northern Europe. Methods Between April 21 and 27, a cross-sectional epidemiologic study targeting the full population of Ischgl (n = 1867), of which 79 % could be included (n = 1473, incl. 214 children), was performed. For each individual, the study involved a SARS-CoV-2 PCR, antibody testing and structured questionnaires. A mathematical model was used to help understand the influence of the determined seroprevalence on virus transmission. Findings The seroprevalence was 42.4% (95% CI 39.8–44.7). Individuals under 18 showed a significantly lower seroprevalence of 27.1% (95% CI 21.3–33.6) than adults (45%; 95% CI 42.2–47.7; OR of 0.455, 95% CI 0.356–0.682, p< 0.001). Of the seropositive individuals, 83.7% had not been diagnosed to have had SARS-CoV-2 infection previously. The clinical course was generally mild. Over the previous two months, two COVID-19-related deaths had been recorded, corresponding to an infection fatality rate (IFR) of 0.25% (95% CI 0.03–0.91). Only 8 (0.5 %) individuals were newly diagnosed to be infected with SARS-CoV-2 during this study. Interpretation Ischgl was hit early and hard by SARS-CoV-2 leading to a high local seroprevalence of 42.4%, which was lower in individuals below the age of 18 than in adults. Mathematical modeling suggests that a drastic decline of newly infected individuals in Ischgl by the end of April occured due to the dual impact from the non-pharmacological interventions (NPIs) and a significant immunization of the Ischgl population. Funding Helmholtz Association, European Union’s Horizon 2020 research and innovation program, German Research Foundation (DFG), state Tyrol.