Rapid tests fail: Covid-19 rapid tests deliver unreliable results – knowledge


Covid-19 rapid tests are said to be a pillar of infection protection in Germany. However, according to a current analysis by the “Cochrane International” research network, only a few of the rapid tests available reliably detect infections.

According to the resolutions of the federal and state governments, daily tests should become mandatory where it is difficult to keep your distance or to wear a mask. Before air travel to Germany, the obligation to test should be stipulated in the Infection Protection Act and two tests per week should be possible for schoolchildren, teachers and daycare workers. Positive test results indicate who should immediately limit their contact with other people in order not to infect them.

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“If an employee in a nursing home tests himself before going to work, he will prevent many secondary infections in the event of an undetected infection,” said Michael Meyer-Hermann from the Helmholtz Center for Infection Research in Braunschweig, the Tagesspiegel. “The purpose of the tests planned here is to interrupt chains of infection,” says the systems immunologist.

Positive test results are also intended to help people receive medical treatment and quickly track their contacts. However, the tests can detect symptomatic diseases quite reliably, but many do not provide reliable results before the onset of the first signs of the disease, said Cochrane International. The overview study was published today.

Anyone who is not infected will get an accurate result

Rapid tests provide a result within 30 minutes to two hours. Smears from the nose or throat are used as sample material. Antigen tests work if they contain virus proteins, for example fragments of the envelope. Rapid molecular tests identify the pathogen’s genetic makeup.

The research network comes to a negative conclusion about the accuracy of the procedures. There are big differences, but “very few” rapid tests meet the requirements of the World Health Organization, according to the press release.

The scientists evaluated 64 studies in which the results of rapid tests were compared with those of PCR tests. PCR tests also reveal the genetic makeup of the virus. The laboratory procedure is considered the gold standard, but results are usually only available after one or more days. Only three of the studies, mostly conducted in Europe or the USA, assessed test results in people without symptoms of Covid-19.

The antigen tests detected an average of 72 percent of those infected with symptoms. If the tests were done with symptoms in the first week, the detection rate was 78 percent. The results for tests from different manufacturers ranged from 34 percent to 88 percent. However, the outcome also depends on how well the instructions for the procedure were followed. In infected people without symptoms, the antigen tests only gave the correct, positive result in an average of 58 percent of the cases. According to the quality criteria specified by the WHO, however, tests must detect at least 80 percent of those infected.

Negative test results, on the other hand, were met with great accuracy: in 99.5 percent of those tested with symptoms similar to Covid-19 and in 98.9 of those tested without symptoms. Here, the WHO criterion of at least 97 percent correctly negative results is mostly achieved.

Database for test strategy is missing

For infection protection, however, it would be more important to reliably identify infected people. “Ideally, two people who want to meet would test each other in a standard and uncomplicated way beforehand and then sit together, relaxed, without a guilty conscience or worrying about getting infected or infecting the other,” says Meyer-Hermann. However, there is no certainty of a correctly negative result, especially as long as no symptoms occur.

“In all antigen tests, some infected people will slip through,” says Jac Dinnes, one of the Cochrane authors from the University of Birmingham. It is therefore important that a negative test result also communicates that infections cannot be ruled out.

The evaluation also questions the extent to which standard tests, for example in schools and nursing homes, can help protect against infection. “We haven’t found any data or studies on it that assess the accuracy of repeated tests on people who are unknown about their exposure to the virus,” says co-author Jon Deeks of the University of Birmingham. “This test strategy is introduced without the basis of real application data.”

However, the study found that the accuracy of the results is also affected by who is doing the test. In further investigations, the connection between experience with the tests and their sensitivity will be examined more closely.

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Rapid tests fail Covid19 rapid tests deliver unreliable results knowledge


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