You performed a susceptibility study of antigenic tests for coronavirus at the Motol University Hospital. What did you find out?
We set ourselves the goal of simulating a situation close to surface testing. So use an antigen test to test people who come to our hospital’s collection site. After all, this is somewhat different from the concept of surface testing, because most of the subjects came to the sampling point from some indication. About half of the people reported symptoms close to covid-19, half were asymptomatic. In the end, however, we obtained a relatively representative sample of the population, which we tested in parallel with the standard, reference PCR method and antigen test. The study showed that the antigen test could detect infection in two-thirds of those who passed the positive PCR test.
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This means that the sensitivity is somewhere around 70%, and therefore that out of 10 infectious patients, three will not come out. Regardless of the antigen test used. We deliberately tried two to avoid possible mistakes, but more or less agreed.
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Did you also take into account that PCR tests may have been false positive in some cases?
I do not think that this has happened, although it is an absolutely adequate remark, that is, to take into account whether PCR tests do not overdo it. However, we have to rely on something to evaluate the study, and at this point we are relying on a reference method, which is PCR.
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We had 222 positive seizures, of which 168 had symptoms, so it was suggested that they may have a coronavirus infection. There were 54 asymptomatic patients left, but most of them were shaken. We can conclude from this that the finding of PCR positivity is not accidental and that these people are really positive. Moreover, there were no cases of repeated testing at the end of the disease, so we did not have to solve the problem of persistent positivity. But of course, as a true scientist, you must always consider the risk of false positives.
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Does this mean that these antigenic tests would not be very suitable for general testing, as planned by the Ministry of Health?
It is offered. It should be noted that the antigen test is not designed as a screening test. Even the manufacturers themselves say that it should not be used headless. Read the antigen test leaflets for use in patients with symptoms of covid-19. This has its logic, because to obtain a positive result, a relatively high viral load is required, which is present in the symptomatic patient. In connection with the diagnosis, it is also worth noting that antigenic tests are nothing new in the diagnosis of infectious diseases.
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We have experience with them, for example, in the diagnosis of influenza, where they were widely used in the past, but their sensitivity ranged between 50-60 percent. It is therefore no big surprise that even an antigenic test for a new coronavirus has a sensitivity in this range.
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The idea of comprehensive population testing has been abandoned, but the state wants to test nursing homes in this way.
Comprehensive testing of seniors is actually targeted testing, which is performed for clear, preventive reasons. We are trying to prevent the outbreak of the epidemic in high-risk groups of the population and we need to detect the first cases in time. Preventive testing of defined groups has its justification.
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But are antigenic tests suitable for it?
According to our data, if testing is done in this way once, they are not suitable, because 30 percent of people will not be caught and the epidemic will not be stopped. You only slow it down because you isolate seven out of ten people, but not three. However, if you test repeatedly, you already reduce the risk of leaks, that is, if you test the same individual often enough. The question is how often to repeat testing. There is talk of a frequency once a week, but it is possible that such a frequency is insufficient precisely because false negative cases may go unrecognized for too long. I can imagine that when tested once every three days, the antigen test could be more beneficial.
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| Antigenic tests detect the presence of antigens, which are specific proteins that appear on a sample from the respiratory system if the virus is currently actively replicating. Therefore, this test is suitable for detecting ongoing infection. It is performed by swabbing from the nasopharynx. No laboratory is needed for evaluation, the result is known within 30 minutes. However, the reliability of the antigen test is affected, for example, by the concentration of the virus or the time since the onset of the disease. Some infected may not be detected. |
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Some companies already offer test kits for purchase for home use. How do you look at it?
I look at it quite reservedly. To perform the antigen test we used in our study, you need a nasopharyngeal swab. Anyone who has tried such a swab on their own skin knows that it is a relatively painful, unpleasant procedure, ie it is not a trivial sampling that everyone could just do correctly in the comfort of home. There are now reports that saliva or other more freely available material could be tested, which would be flawless, but it is necessary to verify that the results of the examination of such material would correspond to the results from the nasopharyngeal swab.
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Most of these commercial tests are antibody tests?
Antibody tests are about something else entirely. We do not use them to diagnose the disease, but to trace back whether the patient has had an infection or not. We went through the stage of poor indications of antibody tests in the spring, when we used them for a short time as rapid tests with the assumption that they would lead to the diagnosis of patients, as shown by publications from China. In our country, their use has not proved successful.
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It is outside your field, but what is the current situation in the Motol hospital?
Fortunately, it can be said that so far no critical situation with beds, even with a large number of patients in a difficult condition, is taking place.
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