Infected or not? So sure, the Corona-Tests

All eyes are on the number of Corona-Infected. However, it is also clear that there is a significant underreporting of non-scheduled cases. Studies in several regions of Germany to gain a better Overview. From the biotechnology center of the pharmaceutical giant Roche in the upper Bavarian Penzberg an antibody test, the to bring Chairman of the Board, Christoph Franz, according to the world millions of times clarity comes now.

However, because there is no in all respects, one hundred percent reliable Test, the results of such investigations to be provided with a question mark. “There is a big gray area,” says Antonia Zapf from the Institute for Medical biometry and epidemiology, University hospital Hamburg-Eppendorf. The Numbers and studies would have been a good impression of the development. “It is not important to communicate that the figures are estimates – the truth.”

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Important specificity and sensitivity are

How reliable a Test is working, provide the manufacturer with values for specificity and sensitivity. The sensitivity for the detection rate, i.e. the percentage of patients in which the infection is actually detected. A Test with a sensitivity of 95 percent not identified 95 out of 100 infections, and 5. For the Roche Test, Elecsys Anti-Sars-CoV-2, the sensitivity is according to the company, 100 percent. Board of Directors President Franz spoke on Monday of a completely “new quality level”.

The specificity tells you how many Healthy people, who are definitely not infected with the Virus, or were to be detected by the Test, are actually considered healthy. A Test with a specificity of 95 percent returns in 5 out of 100 non-infected people mistakenly get a positive result. For the Elecsys Anti-Sars-CoV-2, Roche, indicates the specificity of 99.8 percent. In the case of high sensitivity and low specificity, there can be many false-positive findings.

A distinction must be made in the testing, furthermore, whether it is a detection of the genome of the Virus Sars-CoV-2 or an investigation on a specific antibody, developed by the Affected after infection with this Virus. For current infections, the Coronavirus is detected according to the Robert Koch Institute (RKI) molecular biologically by smear about a Revenge after the genome of the Virus (RT-PCR).

Problem: false-negative and false-positive Tests

“There have been developed several different test systems, each with certain genetic sequences of the pathogen recognize”, and explained the Bavarian state office for health and food safety (LGL). Specificity and sensitivity were, among other things, by the gene segment, or the combination of Gene segments – but also the used RT-PCR reagents, the LGL. Laboratories are therefore working with different test systems and related responsible for for the required materials.

Tests on a Sars-CoV-2-specific antibodies in the blood as well as Roche’s Elecsys Anti-Sars-CoV-2 for the diagnosis of acute infection has no role, because between the onset of symptoms and the detectability of specific antibodies according to the RKI information about seven days, in individual cases, and more. The crucial factor is the distance between the disease and the Test is therefore, as Zapf explains. The larger this period is, the lower the probability that the RT-PCR is positive and the greater the likelihood that the antibody test is positive was.

It becomes problematic in the case of so-called false-positive or false-negative results. Simply put: if so, the result is not displayed corresponds to the facts. The consequences are different, depending on whether it is a virus detection by RT-PCR or antibody detection.

Which Test is better?

In the case of the RT-PCR negative results were mainly false-fatal, so Zapf, since this means that the Tested are classified as healthy, even though they are infected. The Professor makes it clear: “That is, Yes, people go out and plug in maybe others.” In the case of false-positive Tests, the people and contact people in quarantine would have to, what would actually be unnecessary. But in case of doubt, the whole of society, the lower level of damage considered.

In contrast, the consequences of a false-positive finding, in your view, are the anti-body test more severe, because people feel wrongly safe and may not, for example, hygiene regulations and contact restrictions.

For this purpose, a sample calculation: we assume that 83 million people in Germany would be infected a Million and a Million would be recovered and developed antibodies. In the case of a full survey with Tests (RT-PCR and antibody test) with a sensitivity and a specificity of 95% 50,000 Infected would be diagnosed falsely as a healthy and 50,000 incorrectly as well. More than four million people would, in turn, a false positive result – think they were infected, even though they are healthy. And the antibody test would lead to about four million in false negative results.


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Beware of Tests from the Internet

Added to this, according to data from the Paul-Ehrlich-Institut as the Federal Institute for vaccines and biomedical pharmaceuticals that the manufacturer Covid-19-certify Tests until may 2022 self. About the reliability of rapid tests, the authority could therefore make no statement, “because the appropriate studies have not been done yet”. The Covid-19-antibody tests should be excluded, furthermore, a possible cross-reaction with antibodies formed against other corona viruses.

The Institute also points out that the validation of Tests, such as those offered in the Internet, is not assured because of the existing possibility of “Self-certification” always. “Demonstrably, there are also forgeries of certificates.”

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