The significance of corona mass tests

Scientists of Danube University Krems, in cooperation with other research institutions, investigated the significance of mass tests

20/11/2020

The results of two Cochrane reviews show that 20 to 70 per cent of COVID-19 infected persons slip through the rapid antigen tests, depending on their quality. These results suggest that one-off mass tests only have a manageable significance. Only regular testing can provide accuracy on the actual infection status.

Following the current lockdown, the federal government plans to conduct SARS-CoV-2 mass tests in Austria. The aim is, among other things, to identify and isolate infected people yet without symptoms in order to break the chain of infection as a precautionary measure. However, Cochrane Collaboration recently published two systematic reviews, which evaluate the usefulness of mass testing to contain the COVID-19 pandemic, with scepticism. The researchers at the Department for Evidence-Based Medicine and Evaluation of Danube University Krems contributed to one of the reviews.

This review investigated the effectiveness of different mass tests or screenings (e.g. laboratory tests, checking body temperature) to contain the pandemic and clearly indicated that one-time testing of large population groups showing no symptoms is deemed futile. The second review conducted the significance of rapid tests. These include antigen tests, as they are intended for mass screening. These performed poorly. Rapid antigen tests missed detecting between 20 to 70 per cent of people infected depending on quality, procedure and implementation.

Limited security

On the one hand, one-time antigen tests are a snapshot and might create a feeling of presumed safety for those examined. Only regular testing can provide accuracy about the infection status. Regular testing only has an effect on the spread of the pandemic, if people tested positive self-isolate in a reliable manner.

The uncertainties of rapid antigen tests have been calculated based on these findings: If, for example, five million people showing no symptoms were tested in Austria, around 100,000 people would have to be isolated due to a possible false positive test result. At the same time, about 6,000 asymptomatic but infected persons are overseen in a single test. They are false negative and can continue to infect other people. The assumptions of the Municipal Department 15 Health Service of the City of Vienna regarding the quality of rapid tests lay the basis for this calculation. According to these assumptions, the planned antigen test does not work for 20 per cent of infected persons and two per cent get a false positive result. The Federal Ministry of Education, Science and Research conducted a study ("Gurgelstudie") in which the infection rates among teachers was reported and on the bases of which it is assumed that 0.6 per cent of the population without symptoms unknowingly carries SARS-CoV-2.

Regular tests and contact tracing

Prof Gerald Gartlehner, Director of Cochrane Austria at Danube University Krems, states: "Mass tests can be quite useful in particular risk groups, for example in the care sector. But, they must be carried out regularly. Whereas testing the healthy population on a one-off basis is questionable. People should know that mass tests do not suggest complete safety and can also have negative effects."

Barbara Nußbaumer-Streit, Deputy Director of Cochrane Austria at Danube University Krems, adds: "It would be better to invest resources where really needed, i.e. in testing sick people and tracking their contacts. It is suspected that mass testing will put even more strain on the system."

 

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