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
Plain Language Summary The Austrian ski resort of Ischgl was a major hot-spot of SARS-CoV-2 infection early on in the pandemic. Here, we investigated the number of people that had been previously infected with the virus in Ischgl in April 2020, by measuring antibodies, blood proteins produced in response to the virus, against SARS-CoV-2. We found that these antibodies were present in 42.4% of the individuals tested and that the majority of these infections, which were generally mild, had not been previously detected. Children were less likely to have these antibodies compared to adults. Using mathematical models, we also found that the subsequent decline in SARS-CoV-2 infections was likely caused by a combination of immunity in the population of Ischgl and of non-pharmaceutical interventions. Our findings allow a better understanding of localised outbreaks of SARS-CoV-2 and how these might be controlled in future.
Knabl et al. perform a seroepidemiological study in the Austrian ski resort Ischgl, where a super-spreader event lead to a SARS-CoV-2 outbreak. Through mathematical modelling, they find that the subsequent decline in viral transmission was most likely a combined effect of high seropositivity and the implementation of non-pharmaceutical interventions.