||NIH COVID-19 Scientific Interest Group
In early March 2020, a SARS-CoV-2 outbreak at a ski resort in Ischgl, Austria, initiated the spread of SARS-CoV-2 throughout Austria and Northern Europe. Thousands of infections can be traced back to Ischgl. In a recent study by Medical University of Innsbruck investigators, 42.4 percent of those living in Ischgl were shown to be carrying the new coronavirus antibodies, indicating they had been infected in the COVID-19 pandemic. Between April 21 and 27, a cross-sectional epidemiologic study targeting the full population of Ischgl (n= app. 1,867), of which 79 percent could be included (n=1473), was performed. For each individual, the study involved a SARS-CoV-2 PCR test for the virus, antibody testing, and a questionnaire. In addition, the SARS-CoV-2 PCR+ cases reported to the authorities were included. The seroprevalence was 42 percent and individuals under 18 showed a significantly lower seroprevalence (27 percent) than adults (45 percent). However, only 105 study participants remembered if they had a previous positive PCR result. The clinical course was generally mild and only two individuals in Ischgl had died from infection corresponding to an infection fatality rate (IFR) of 0.26 percent. In the first week of April, a public screening in Ischgl had found 19 percent of the population to be PCR+. However, only 8 (0.5 percent) individuals were newly diagnosed to be infected with SARS-CoV-2 during the study conducted 2-3 weeks later. Ischgl was hit early and hard by SARS-CoV-2, which led to a high local seroprevalence of 42 percent, that was lower in individuals below the age of 18 than in adults with a low IFR. As nonpharmaceutical interventions (e.g. social distancing, mask wearing) had already reduced virus spread, mathematical models conclude that the high seroprevalence significantly contributed to the drastic decline of new infections during April.