On 20 October 2020 Slovenian TV presenter Marko Potrč claimed in his Facebook post that the tests performed to detect the presence of the virus (PCR) do not tell if someone is actually infected or even contagious. He said that dr. Lejko Zupanc, infectious disease specialist, also had to admit this on national television. This statement is misleading and thus mostly false.
Marko Potrč is a Slovenian TV presenter, who became more active on social media, particularly on Facebook, during the global pandemic. His first post that went viral was published in the beginning of July. He is focusing on criticising government measures which also results in undermining the health professionals and their work. While constantly posting he gained a lot of supporters and sympathizers. His huge reach (more than 1,000 likes on post) and audience engagement also led to mentioning him in mass media.
In the previously mentioned Facebook post he is defending himself by answering to the public and expert’s criticism regarding coronavirus – measures and the virus itself. He explains himself by giving 13 statements – the claim we factchecked is one of them. In this particular post, he does not draw from opinions of professionals. The first person we contacted in the process of factchecking was the author himself. We wanted to get information about the motive that drew him to make the post and the original sources on which the claim was based. Unfortunately, we did not get his reply.
As the author of the claim Marko Potrč is not an expert on this topic and because of the current panic around the pandemic and tests, we deemed it appropriate to get professional and scientific opinions on the matter. In his post Potrč is leaning on a statement of dr. Tatjana Lejko Zupanc, the head of Clinic for Infectious Diseases and Fever Conditions Ljubljana, in an interview for national television Let’s beat COVID-19. It must be pointed out that Potrč only used a small part of her statement and ignored her further explanation. Because of this we contacted her to get her response and explanation on this topic. Additionally we contacted another expert, an infectologist who wishes to stay anonymous. He is currently working as an infectologist at the COVID department, while the amount of attacks on medical staff is getting more and more intense, therefore he wishes not to be judged based on his medical opinion.
Being infected VS. being contagious
Firstly, the distinction needs to be made between being infected and being contagious. “An individual with whom the occupation occurred has become infected. According to the Slovenian Medical Dictionary, an infection is “the intrusion of pathogenic organisms (viruses, prions, bacteria, fungi, parasites) into the body and their reproduction, which may or may not be followed by clinical signs of disease. Being contagious means that one individual is able to spread his infection to others,” the infectologist explains.
What do PCR tests actually detect?
According to our second expert, dr. Lejko Zupanc, the PCR tests are being used to prove the presence of the virus’ nucleic acid. ‘’As long as the nucleic sequence (in this case SARS CoV2 virus RNA) is present in the sample in a sufficiently high number, it will be detected by a PCR test. However, the method itself cannot distinguish between nucleic acid from active microorganisms and nucleic acid from inactive (‘dead’) microorganisms that can remain in the body after overcoming infections,’’ adds the infectologist.
The amount of virus and its activity can be checked by additional methods. ‘’There are ways in which we can predict the viral load from the result of PCR testing, namely the number of CT (Cycle Threshold). The higher this number, the less nucleic material is in the sample being examined, the less likely a patient is to be actively infected or contagious,’’ explains the infectologist. This information can help the professional in deciding what stage of the disease the subject is in.
Both of our experts agree that the laboratory results must be interpreted with the full clinical picture of the patient. ‘’If someone has clinical signs and a positive PCR test this is evidence of the disease. If someone has no clinical signs and has appropriate epidemiological data and a positive PCR test he is infected, the infectivity level can not be judged, it may or may not be present. For safety reasons we believe that a person is still spreading the virus. If someone had covid some time ago and has no clinical signs and a positive PCR test, we can consider it to be a residual virus which means that a person is not contagious at the moment,’’ says dr. Lejko Zupanc. ‘’The first rule of interpretation of any investigations in medicine is to interpret them together with the clinical picture,’’ explains the infectologist.
Conclusion
In short the PCR test is currently the most sensitive and specific test on the market to detect the presence of the virus. However, it only tells us that the desired nucleic sequence is present in the body, which means that the person has been in contact with a microorganism. The test solely does not tell us if the person is actively infected or even contagious, but the test must always be interpreted with a full clinical picture or additional tests. Therefore we find Potrč’s statement misleading and we rate it as mostly false.
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