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Virenlast. Should the sample be taken for a rapid Covid-19 test in the nose or by mouth?
For Michael Janisch this question does not arise; at least not then if you want to get correct results. “With a throat swab, the error rate for false negatives is up to 90 percent,” says Brigadier, who heads the Office of Weapons and Defense Technology (ARWT). In other words, if the sample is only taken in the mouth, there is a 90 percent risk that the patient appears healthy, but is actually sick.
Several responsible factors
Heinz Burgmann, Head of the Department of Infectious Diseases and Tropical Medicine at MedUni Vienna, this percentage seems very high. “Several factors are responsible for an accurate test result: where and how the sample is taken, and what stage of the disease the person performing the test is currently in. Antigen tests, for example, react positively when the virus load is very high. “
But why can an institution like the ARWT make such statements? The ARWT is the Army’s 1450 Internal Hotline. Here, as more recently Minister Klaudia Tanner, all cases and suspected corona groups that occur in the army are verified. If that’s not enough, the ARWT does what civil society organizations cannot currently do: Sick people are tested during the course of illness. “Up to seven times per patient,” says Janisch. “So we also know how the virus load changes over time.”
Correct sampling
Janisch explains the extremely high susceptibility to errors with the fact that Covid-19 starts in the nose and the corresponding viral load can be found there. The infectiologist Burgmann even puts it in perspective: “If the virus has migrated to the lungs, a nasal swab is not the gold standard either. “
Also: the correct throat swab in the mouth is difficult. “A small scratch on the cheek is not enough, you have to dig deep into the throat to get a good sample – usually only specialists like those in hospitals can do that,” says Janisch. It involves the back of the throat. Burgmann explains where the uvula is located. For a nasopharyngeal swab, the collection rod is inserted four to five centimeters into the nose. “Not only should you reach the nasal mucosa, you also try to penetrate the nasopharynx.”
Recognize infections
Regarding rapid tests, Janisch cautions against overestimating their detection power: “These tests were developed to quickly determine if they have Covid-19 or another disease in patients who have clear symptoms. They were not designed to find asymptomatic patients. “
¿Why is it so important? Unlike the PCR test, the rapid test “only” looks for virus proteins. The bottom line: The concentration of these proteins fluctuates during the course of the disease, and this means that tests sometimes give a “negative” result, even if someone is positive for Covid-19 according to the PCR test. Burgmann: “That is why it is important to catch the infectious phase to break the chain of infection. “
