The number of confirmed infections with SARS-CoV-2 is a central figure for decision-makers and the public. For most countries, it is safe to assume that the number of unreported cases (“dark figure”) is a multiple of the confirmed cases. It is essential to estimate a total prevalence including unreported cases – on the one hand to learn more about central parameters such as case fatality rate, on the other hand to plan and refine decisions about measures with regards to the pandemic.
PCR-tests in a nationwide representative random sample
The Austrian Ministry of Science launched this study to determine the spread of SARS-CoV-2 including the “dark figure” in Austria. It is the first study in continental Europe based upon nationwide PCR testing in a representative random sample. Self-selection into the sample was not allowed, and various strategies have been applied to limit sampling bias and non-response which led to a substantially higher participation rate than in comparable studies.
Key results
PCR tests (cobas® SARS-CoV-2) were carried out in the period April 1–6, 2020. 1,544 cases have been included in the final analysis.
- 6 respondents have been positively tested.
- The proportion of positively tested in the final weighted sample is 0.33%. This proportion represents about 28,500 individuals among the Austrian population, excluding those currently in hospital.
- Applying a 95% confidence interval for the proportion of positively tested results in a range between 0.12 and 0.77% or between 10,200 and 67,400 individuals in absolute terms.
Project consortium
Commissioned by: Republic of Austria, represented by the Federal Ministry of Education, Science and Research (BMBWF).
Project consortium:
- SORA Institute for Social Research and Consulting (project lead, co-ordination, sample, data analysis), closely co-ordinated with:
- Institut für statistische Analysen Jaksch & Partner GmbH (hotline, sample management, telephone interviews)
- Medical University of Vienna(evaluation of PCR tests)
- Complexity Science Hub Vienna CSH (statistical-medical expertise)
Directly commissioned by the BMBWF:
- Austrian Red Cross and its national associations (carrying out PCR tests throughout Austria)