Rapid antigen test misses many symptom-free Covid carriers

The rapid antigen test detected only 44% of PCR-positive people © Keystone / Gaetan Bally

The rapid antigen test approved in Switzerland has performed badly in a direct comparison with PCR tests. Among 141 people infected with Covid-19, it detected only two out of three infections.

The rapid test performed even worse in symptom-free infected persons: it detected only 44% of PCR-positive people.

The results published in the International Journal of Infectious DiseasesExternal link deviate considerably from the manufacturer’s data, the Insel hospital and the University of Bern said on Thursday.

The research team determined the diagnostic accuracy of Roche’s rapid antigen test in a clinical setting for the first time by evaluating samples taken by specially trained experts using both test methods.

In the sample of 1,465 tests, the PCR test showed that 141 people (9.6%) were infected with Covid-19, while the rapid antigen test detected 95 infections (6.4%). In practice, it could be assumed that the results are even worse, especially when taking samples, the statement said.

“Widespread application in such a setting might lead to a considerable number of individuals falsely classified as SARS-CoV-2 negative,” the study concluded.

Missed cases

Co-author Franziska Suter-Riniker from the University of Bern added that antigen tests work better with a high viral load than with a low viral load. Thus, highly infectious people would also be more likely to test positive.

The researchers wrote that currently an estimated 130,000 rapid tests are carried out per week in Switzerland. With about 18% coming back positive, some 23,400 would be correctly identified as positive, but 12,400 infected people would be missed.

“There is thus a potential risk that antigen tests will make the pandemic worse instead of slowing it down,” said study leader Michael Nagler from the Insel hospital. “The rapid antigen tests available today should therefore only be used with reservations as part of the Covid-19 measures.”