2023-09-19 16:45:12
Rapid antigen tests for Covid “can certainly be a weapon of awareness. I suspect” of having been infected, “I take the test, I’m negative. Or I find myself positive and stay away from grandparents, from fragile relatives, even from those he is young but unfortunately he is seriously ill, he suffers from immunosuppressive diseases, he cannot be vaccinated and if I were to infect him the risk would be enormous. In this function, the test has a logic”. This was stated to time.news Salute by Pierangelo Clerici, president of the Association of Italian Clinical Microbiologists (Amcli), who takes stock and offers some advice on when to use the rapid swab, how to do it and with what reliability. The first point is that “the tests work and the constant monitoring of the variants and the surveillance that all the Regions constantly carry out work, also on the basis of what was decided in the latest circular of 31 August regarding checks in hospitals, in RSAs , in the communities. We are active at a national and regional level”, assures the expert.
“The functioning and effectiveness of the tests – he specifies – are monitored periodically. There is a list of tests that is licensed in Europe by the ECDC authority”, European Center for Disease Prevention and Control, “which monitors the tests that come out on the market”. So what is important to check? “That they are always CE marked products”, an element that indicates the conformity of a product with EU regulations, Clerici lists, “and that they have validation prior to numerous cases. But verification is always there from this point of view Also because we find ourselves with a market that is 85% of antigenic products on the Chinese, Korean and South-East Asian markets. Therefore checks need to be carried out. While on the European market the checks are not carried out post, but before, that is, during the preparation of the product. Then there is a gray area which is online purchases and there we don’t know what happens. It is therefore better to still turn to sellers who know what they are offering.”
In general, what is the level of reliability of the rapid antigen test? “If the sampling is carried out correctly and with a certified product – points out the Amcli president – we can say that we can even reach peaks of 92% accuracy and sensitivity, but to get there the entire system needs to be in place, from the sampling phase to the of the reading, is carried out in a competent manner. Antigenic tests are also used in hospitals, but they are those tests that were once called ‘fourth generation’, that is, based on innovative technology: they have an automatic reader and the test highlights an immunofluorescence of the reaction that occurs, therefore not just the colored band of normal tests. In that case, the sensitivity even rises to 97% but this test is the prerogative of hospitals or large centres”.
THE PADS AND THE NEW VARIANTS
Is there a risk that new variants of Sars-CoV-2 – such as Eris EG.5 or the highly mutated Pirola BA.2.86 – are more ‘invisible’ to rapid antigen tests? “There are no reasons to think so. Because antigen tests are based on the search for pieces of ‘immutable’ antigen. We can say that in particular there are some parts of the antigen that vary, and they are those of the new variants that we have learned to know, but let’s also say that, from Omicron onwards, all the subsequent ones are its subvariants. So today the problem is not whether the antigen test recognizes the variant or not. The question to ask is another: is it useful to do the antigen test or no? The current indications narrow the field to a few people” for whom it is important to do so. “The ‘buffer factory’ that we remembered in 2020-2021 no longer makes sense”, highlights the president of the Amcli.
“The ministerial circular issued at the end of August – recalls Clerici – defines the categories that must be subjected to the Covid test. And in any case the molecular test”, the classic swab that is done in laboratories, “is” the reference test. “It is also true that if someone wants to get tested they go to the pharmacy or supermarket, buy the rapid test and can do it. But the rapid test does not have the sensitivity of the molecular test, so very often it turns out negative even if it is positive. For truly at-risk categories, therefore, the ideal would be to undergo a molecular swab if there is suspicion of positivity.” But we are talking about restricted categories. “The swab factory no longer makes sense today thanks to two reasons: the circulation of the virus which has existed in recent years and has caused many people to become infected and produce natural immunity, and vaccinations. Who remains outside of this situation? They are the highly fragile, those who perhaps have not been able to get vaccinated”, says Clerici.
Any false negatives, according to the expert’s message, are not linked to the fact that the rapid antigen tests do not recognize the new variants, but rather to the sensitivity of the test or to any errors in its execution. And here “we open a delicate chapter – observes Clerici – With Covid we have also implemented the self-test”, the quick ‘do it yourself’ swab.
“People did it on their own, but we must never forget that to be done well, the swab should necessarily be done both at the pharynx and nasal level. Doing it only nasally already reduces sensitivity. And furthermore, if the test is not a molecular, the sensitivity is further reduced. Therefore, if you have to play with the antigen test, which is legitimate, it is better to have the sample taken by an expert, who could be a nurse or a doctor in this field. Not for example the pharmacy clerk or the uncle who is at home with us. Because doing the swab properly is not easy, and it is always an ‘invasive’ act.”
“The functioning and effectiveness of the tests are monitored periodically”, clarifies Clerici. “And we also need to clarify one point. We have been saying it for years and it must be remembered: the variants will never cease, indeed they will increase in number, but it is in the logic and biology of the virus and we must not be frightened when further ones arrive. Because it is the tracking of the new variants which allows us to say that with the vaccinations carried out, and with those that will be carried out from October for those who want, there is also coverage of the new versions of the virus.
“Let’s not worry about the number of variants. At most, let’s worry about the spreadability of Sars-CoV-2. In this case it is right to monitor and keep the situation under control. But – the microbiologist points out – we are not surprised that in this period there is an increase of cases and it is not excluded that there may also be an increase in the next autumn-winter, as is right to be expected given that Covid is a disease that affects the respiratory system. Just as there will be the flu, there will also be an increase in Covid. What we see and what comforts us is that there are no serious cases. And this is the important fact, we must get away from the logic according to which there is a lot of Covid and we are at risk of ending up in intensive care.” According to the Amcli president, it can rather be said that “there is a lot of Covid, but fortunately we are protected through natural circulation and immunity given by vaccination. And the tests work”.
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