High SARS-CoV-2 seroprevalence in children and adults in the Austrian ski resort of Ischgl

Abstract

Background In 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 21st and 27th 2020, 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. Results The seroprevalence was 42.4% (95% confidence interval (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 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. Conclusions 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 occurred due to the dual impact from the non-pharmacological interventions and a high immunization of the Ischgl population.

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

“…Coronavirus disease 2019 (COVID-19) caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was first detected in December 2019 in Wuhan, province Hubei, China [ 1 ] and spread rapidly worldwide including Europe [ 2 ]. Typical symptoms of COVID-19 are fever, persistent cough, shortness of breath [ 1 ] and many patients also experience olfactory and gustatory dysfunctions [ 3 , 4 ]. Symptoms are present at different ages, with varying frequency and severity [ 1 , 5 , 6 ].…”

“…Symptoms are present at different ages, with varying frequency and severity [ 1 , 5 , 6 ]. While the majority of cases show mild or even no symptoms, a proportion of cases often with comorbidities require intensive care unit (ICU) admission and/or prolonged mechanical ventilation [ 1 , 3 ].…”

“…In Austria, the first two confirmed COVID-19 cases, an Italian couple entering from Lombardy, Italy, were diagnosed in Innsbruck, Tyrol on 25 February 2020 [ 7 ]. Following an outbreak in the skiing area of Ischgl, Tyrol, [ 3 , 7 ] and a steep increase in documented SARS-CoV-2 cases in the whole federal state in the first half of March 2020, comprehensive preventive measures were put in place, including quarantine of all municipalities in Tyrol. The number of SARS-CoV-2 cases plateaued in the end of March at a 7-day incidence rate of 150–160 cases per 100,000 inhabitants and subsequently declined with very low rates from May until July 2020 (< 5 cases per 100,000 inhabitants), before steadily rising again thereafter [ 8 ].…”

“…Altogether, from March to September 2020, health authorities identified 4536 cases, corresponding to 0.6% of the total population in the state of Tyrol ( n = 757,634); however, given limited testing capacities during the first epidemic peak, the focus on symptomatic cases or on those with a travel history, and challenges in contact tracing, it is likely that this number is an underestimate of the true burden of disease in the Tyrolean population. For instance, in the skiing area of Ischgl, 42.4% of the population were seropositive, but only one fifth of those had previously been identified as SARS-CoV-2 cases [ 3 ].…”

Survey on “Knowledge and Attitudes Regarding the Coronavirus Pandemic” in the Austrian, German and Swiss population

“…following SARS-CoV-2 outbreaks like in Ischgl (Austria; March 2020) [7]. In the Austrian population, seroprevalence was however not widely tested even as phase 3 of the vaccination plan was launched in April and May 2021 with the start of vaccination among the general population.…”