Fact or fake?

Forum myths: all about corona tests

(Bild: manit/stock.adobe.com)

We are continuing our series on forum myths about corona and are taking the current situation surrounding the previously free corona tests in doctors' surgeries as an opportunity to look at corona tests in general. After all, various conspiracy stories have been circulating about them since their introduction in 2020. We will discuss the most well-known ones below.

Even if coronavirus no longer dominates the news: The following assumptions were particularly prevalent during the peak testing phase:

Claim: Corona tests are not useful and cannot reliably detect corona at all. What's more, they are dangerous and make you ill!

 

Grundlegendes zu den Coronatests

First of all, we need to distinguish between the different types of corona tests. In Austria, there are the following test methods 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 are much simpler, which makes them somewhat less accurate. The advantage is that they can be carried out independently of laboratories. Samples are taken from a nasal or throat swab. There is also the option of a gargle solution. The latter can be less complicated to use and generally more convenient.

• Rapid antigen tests: These tests are also used for acute diagnoses, particularly in cases where it is unclear whether a coronavirus infection is present. In contrast to the PCR tests, they only detect characteristic protein fragments of the virus. This makes them somewhat less sensitive than PCR tests. However, they deliver their results in just 15 to 30 minutes. Especially for regular testing, for example in the healthcare sector, they were an important tool during the peak phase of corona in order to maintain an overview of the pandemic and contain it as well as possible. At that time, they were used in particular to check contact persons and to identify infected persons without symptoms but who were highly contagious.

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

(Bild: Huber Patrick)

Was steckt hinter der Behauptung?

Corona tests, just like everything else surrounding the then completely new virus, were a source of uncertainty for many people who did not know exactly how they worked and did not think they were ill without symptoms. The latter in particular felt as if they had been "tested sick" when they were able to prove that they were infected. This is still often the case today. It is therefore important to familiarize yourself with the following terms when it comes to corona tests:

• Ct value (cycle threshold, roughly translated as "threshold cycle"): Put simply, it indicates how long a sample needs to be analyzed in the laboratory. This is because the sample material is multiplied during the test procedure in order to detect the genetic material of the virus. If this viral material can be detected after a short period of 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 viral material was found. This indicates a lower viral load and therefore a lower infectivity. However, it should be noted that this value also depends on other factors, such as the test variant used or the transportation time. It is therefore not necessarily meaningful on its own.

• Sensitivity: This provides information on whether all sick people are also 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 these people. The other five would be incorrectly classified as not infected ("false negative").

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

(Bild: Alexander Schwarzl)

Behauptung eins

„Die Coronatests sind nicht brauchbar und können Corona gar nicht zuverlässig nachweisen“

Let's take a closer look at the two claims and start with this one. In 2020, Michael Schnedlitz (FPÖ) caused a stir with a dubious "experiment" relating to corona tests. By claiming to have tested positive for coronavirus using a rapid test, he wanted to prove how useless such tests are. However, this absurd demonstration in parliament only proved his lack of education in chemistry. A false positive test for cola is based on the high acid content of the drink and has no connection with the coronavirus. The acid breaks down the protein fragments on the test strip. This destroys the buffer layer and the positive marker becomes 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 a factor
  

  As already mentioned, the different test variants have an impact on this. PCR tests are considered to be very reliable, and trained laboratory technicians are also responsible here. In general, self-tests tend to be less reliable, also because errors can be made by the user. When taking a sample with a cotton swab, for example, there is a risk of getting too few virus particles from the wrong place. In addition, the liquid in a gargle solution preserves the viruses better than the dry cotton swab. However, gargling can also falsify the result if the rinsing time is too short. For this reason, no self-tests were recognized by the authorities or at the border.

• Time of test as a factor
  

  When a sick person is tested also has an impact on the reliability of a corona test. While PCR tests are reliable at any time of infection, even if the symptoms are not yet pronounced, the situation is different with rapid antigen tests, as they are less sensitive and are more likely to reliably detect larger amounts of viral material in a sample. Typical Covid-19 symptoms often only develop around four to five days after an infection. Large amounts of viral material are usually only present in the secretions of the upper respiratory tract from the onset of symptoms. This leads to an increased probability of false negative results.

• Other influences
  As already mentioned, correct sample collection or transportation of the samples also play a certain role, as does the corona variant. This is not the only reason why a second PCR test should be carried out if there is reasonable suspicion of a corona infection (in the event of symptoms or if you are a direct contact person). In the same way, a positive antigen test should be checked by a PCR test.

In summary, no test is 100% reliable. The test result must always be seen in the context of factors such as exposure to COVID-19, symptoms or the current corona numbers. If in doubt, it is therefore best to consult a healthcare professional.

(Bild: APA/Hans Punz)

Behauptung zwei

„Darüber hinaus sind die Tests gefährlich und machen selbst krank“

• Correct implementation as a factor
  

  This was particularly common in relation to the swab tests, as these could sometimes be more painful. There was talk of feared damage to the blood-brain barrier, for example. However, this concern is unfounded. If a smear test is carried out correctly by medical professionals, no serious injuries occur. Although inserting the swab can be painful, this is due to the fact that the nasal mucosa is particularly sensitive to inflammation. Furthermore, the blood-brain barrier is not located in the nose, but in the brain. Between the nose and the brain are, among other things, bones and meninges. Barriers that cannot be penetrated with a simple test stick. If trained personnel carry out the deep nasal swab correctly in the correct channel of the nose, the risks of injury are extremely low. Covid self-tests also use a nasal wing test, where the swab should not be pushed so deeply into the nose.

(Bild: Evelyn Hronek Kamerawerk)

Conclusio zur Behauptung

Whether in the specially introduced test lanes or gargle boxes, in the pharmacy or doctor's surgery or even independently at home: the various testing options served to keep an overview of the number of infected people and to protect vulnerable groups by staying at home after a positive test. After all, a coronavirus infection is also possible without symptoms. While testing was more widespread in 2020 and 2021 due to the situation at the time, the screening programs became more targeted in 2022. In any case, the Austrian testing strategy was regularly re-evaluated and adapted.

It is an untenable statement that corona tests make people ill. The reliability and usefulness of the tests depend on many factors. The latter in particular can also be viewed critically in retrospect. Nevertheless, PCR tests in particular are a reliable means of detecting a corona infection and have had and still have their justification, especially in the health sector.

Again, it is important to obtain information from reliable sources on the current status and remain critical if you are confronted with unproven claims.