Forummythen: Everything about corona tests

Even though Corona is no longer dominating the news, the following assumptions were made, especially during the peak testing phase:

First of all, we must distinguish between the different types of corona tests. In Austria there are the following test procedures that can be used to diagnose an infection with the SARS-CoV-2 coronavirus:

• PCR tests (Abbreviation for polymerase chain reaction test): These tests are used for acute diagnosis in suspected cases and detect the genetic material of the SARS-CoV-2 pathogen. Classic PCR tests are very reliable, but require laboratory analysis and usually take 48 hours. Rapid PCR tests are suitable for faster diagnosis. These use the same method as PCR tests, but significantly simplified, making them slightly less accurate. The advantage is that they can be performed independently of laboratories. Samples are taken via nasal or throat swabs. There is also the option of a gargle solution. The latter can be experienced as easier to use and generally more pleasant.

• Rapid antigen tests: These tests are also used for acute diagnoses, especially in cases where it is unclear whether there is a coronavirus infection. Unlike PCR tests, they only detect characteristic protein fragments of the virus. This makes them slightly less sensitive than PCR tests. However, they deliver their results in just 15 to 30 minutes. Especially for regular tests, for example in the healthcare sector, they were an important means during the peak phase of Corona to maintain an overview of the pandemic and to contain it as best as possible. At the time, they were mainly used to monitor contacts and identify infected people without symptoms but who were highly contagious.

• Antibody tests: Unlike the other two test variants, an antibody test is only used after a SARS-CoV-2 infection. This makes it the drug of choice, especially for people who are not sure whether they have already had Corona or not. It is therefore used to demonstrate that an infection has occurred, but also a successful COVID-19 vaccination.

Corona tests, like everything else surrounding the then completely new virus, were an uncertainty factor for many people who did not know exactly how they worked and thought that they were not sick without symptoms. The latter in particular felt that they had been ‘tested sick’ if it could subsequently be proven that they had an infection. This is still often the case today. It is therefore important to also use the following terms when it comes to corona tests:

• Ct value (cycle threshold, roughly “threshold cycle” in German): Simply put, this indicates how long a sample should be examined in the laboratory. During the testing procedure, the sample material is multiplied to detect the genetic material of the virus. If this viral material can be detected after a short time, this means a high viral load and a low Ct value. Conversely, a high Ct value (around 30) is an indicator that the sample had to go through many rounds before virus material was found. This means a lower viral load and therefore lower contagiousness. However, it should be noted that this value also depends on other factors, such as the test variant used or the transport time. Therefore, taken on its own, it is not necessarily considered meaningful.

• Sensitivity: It provides information about whether all sick people are recognized as sick, or in other words: how well a test can detect the coronavirus in people who are actually infected. In a group of 100 people, a test with a sensitivity of 95% will correctly detect the virus in 95 of those people. The other five would be incorrectly classified as uninfected (“false negative”).

• Specificity: In connection with this, the specificity of a corona test describes how well the test recognizes healthy people who are not infected as such. In our example of 100 people, a test with 98% specificity would show that 98 of them are healthy. The other two would be incorrectly classified as infected (“false positive”).

Now let’s take a closer look at the two statements, starting with this one. In 2020, Michael Schnedlitz (FPÖ) caused a stir with a dubious ‘experiment’ around corona tests. By having Cola test positive for coronaviruses with a rapid test, he wanted to prove how useless such tests were. However, this absurd demonstration in parliament only proved his lack of training in chemistry. A false positive test for cola is based on the high acidity of the drink and has nothing to do with the coronavirus. The acid breaks down the protein fragments on the test strip. This destroys the buffer layer and makes the positive marker visible. The same would happen with a pregnancy test.

In any case, it should be noted that the reliability of corona tests cannot be assessed across the board.

• Test variant as Factor
  

  As already mentioned, the different test variants have an impact on this. PCR tests are considered very reliable; trained laboratory technicians are also responsible for this. In general, self-tests are less reliable, also because users can make mistakes. When taking a sample with a cotton swab, for example, there is a risk that too few virus particles end up in the wrong place. In addition, the liquid in a gargle solution retains the viruses better than the dry cotton swab. However, when gargling, the result may be distorted if the rinse time is too short. Therefore, no self-tests were recognized by the authorities or at the border.

• Test timing as a factor

  Testing a sick person also has an impact on the reliability of a corona test. Although PCR tests are reliable at any time during infection, even if symptoms are not yet pronounced, the situation is different with rapid antigen tests, as they are less sensitive and are likely to be able to reliably detect larger amounts of viral material in an infection. sample . Typical Covid-19 symptoms often only emerge four to five days after an infection. Usually, it is only from the onset of symptoms that larger amounts of viral material are present in the upper respiratory tract secretions. This leads to an increased risk of false negative results.

• Other influences
  As already mentioned, the correct sampling or transport of samples also plays a certain role, as does the Corona variant. This is not the only reason why a second PCR test must be carried out if there is a reasonable suspicion of corona infection (if you have complaints or if you are a direct contact person). Likewise, a positive antigen test should be checked using a PCR test.

In short: no test is 100% reliable. The test result should always be seen in the context of factors such as exposure to COVID-19, symptoms or current corona numbers. If you are in doubt, it is best to consult a doctor.

• Correct execution as a factor

  This was especially common with the stick tests, as these could sometimes be more painful. There was talk of feared damage to the blood-brain barrier. However, this concern is unfounded. If a Pap smear is performed correctly by a medical professional, no serious harm will occur. Inserting the stick can be painful; But this is because the nasal mucosa is particularly sensitive to inflammation. The blood-brain barrier is not in the nose, but in the brain. Between the nose and the brain there are bones and meninges, among other things. Barriers that cannot be penetrated with a simple test stick. When trained personnel correctly perform the deep nasal swab in the correct nasal passage, the risk of injury is extremely low. Covid self-testing also uses a nostril test, where the swab does not have to be pushed so deeply into the nose.

Whether in the specially introduced test lanes or gargling boxes, in the pharmacy or at the doctor’s office or independently at home: the various testing options serve to keep an overview of the number of infected people and to protect vulnerable groups by checking for a positive test. stayed home. Because corona infection is also possible without complaints. While testing in 2020 and 2021 was even more extensive due to the situation at the time, the so-called screening programs became more targeted in 2022. In any case, the Austrian test strategy was regularly recalibrated and adjusted.

That corona tests make you sick is an untenable claim. The reliability and usefulness of the tests depend on many factors. The latter in particular can also be viewed critically afterwards. Nevertheless, PCR tests in particular are a reliable means of detecting corona infection and they had and still have their justification, especially in healthcare.

Again: obtain information from reliable sources about the current status and remain critical when confronted with unproven claims.