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More tests are not the cause of the higher corona numbers

Bwithin three weeks, the number of corona tests in Germany has increased by around half. While 570,746 laboratory tests were carried out in the week from July 20 to July 26, there were 875,524 laboratory tests in the last week from August 10 to 16. According to the figures published by the Robert Koch Institute (RKI) on Thursday, more than ten million corona tests have been carried out since the beginning of the pandemic. The increase in recent weeks, when Federal Health Minister Jens Spahn (CDU) ordered mandatory testing for travelers returning from risk areas, was clear. Numerous new test possibilities also opened up on motorways, at airports and in train stations.

Are the increased numbers of infections only due to the higher number of tests?

No. Increasing the number of tests can lead to an increase in the number of cases as previously undiscovered cases are discovered. However, the increasing number of cases cannot be explained solely by the increased number of tests. If an outbreak suddenly occurs in a district in which the number of reported infections multiplies, as happened in various places in Germany – one would have to assume that the number of tests will also multiply. But this is not the case. According to the RKI, the main reason for the increase in the number of infections in recent weeks are specific infection clusters in individual districts. These were related to larger celebrations, leisure activities, the situation at workplaces, in hospitals, care facilities and refugee accommodation. And more and more with the travelers returning, that is also shown by the news from the municipalities.

The RKI also points out, however, that the tests in March and April and those in the past few weeks took place under very different conditions. In the meantime, testing is done much more independently of suspicion, especially in the new test stations. An illustrative example to refute the thesis that the higher number of cases can be attributed to more tests is the following: In the week from March 30 to April 5, 408,348 corona tests took place in Germany. In the past week from August 10 to 16, more than twice as many tests were carried out with 875,524 samples. While 36,885 positive tests were counted at the beginning of April, there were 8407 positive samples in the past week. The positive rate per test was around nine percent at the beginning of April. An infection is now found in one out of 100 corona tests. Even if a positive test does not immediately mean a person suffering from the coronavirus, as some are tested several times, a closer look at the statistics shows: In the course of spring and summer it has very well happened that the number of tests decreased, but the Case numbers went up – and vice versa.

What role do false positive results play?

The Robert Koch Institute speaks of deliberate false news that is spread in connection with the classic PCR tests with a spatula from the nasopharyngeal mucous membrane. According to this, statements that an infection is falsely indicated in 30 to 50 percent of the tests are simply wrong. In fact, there are false-positive test results. But these are isolated cases. Experts say that the error rate is less than five percent. If in doubt, a second test is usually ordered.

Are the laboratories reaching their capacity limits with the tests?

The longer the corona pandemic lasts, the greater the test capacities. According to the RKI, at the beginning of April, when most of the new infections were reported in Germany, the laboratories were able to carry out around 100,000 tests per day. There are now around 190,000 tests per day. Since the number of transmitting laboratories only increased from 113 to 157 during the period, this also means that the laboratories have increased in effectiveness.

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