Rapid antigenic tests for Covid-19, how they work and how reliable they are

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The spread of the coronavirus is increasing rapidly and faster methods are being sought to test people's positivity. We currently have available two types of tests to identify the presence of the virus:

  • the classic molecular test
  • and the antigen test.

The latter, which can also be performed today at pediatricians and family doctors, allows us to know if a person is positive or negative within 15 minutes. Let's see how the antigen test for SARS-CoV-2 research works thanks to the help of Massimo Clementi, professor of microbiology and virology of the Vita-Salute San Raffaele University of our city

In this article

  • How rapid antigen tests work
  • When it is necessary to do an antigen or molecular test
  • What to do if the antigen test is positive
  • How reliable is the negative antigen test
  • When rapid antigen tests are useful
  • Off to antigen tests in schools

How rapid antigen tests work

"Rapid antigen tests allow us to search for virus antigens COVID-2", explains Dr. Clementi." It is a different way to evaluate the presence of the virus compared to the classic molecular test, but with the advantage of having a result in a very short period of time ".

The classic molecular swab, that is the one most used during the first phase of the pandemic, is characterized by being highly sensitive, but its analysis requires long times and at the moment we cannot afford to waste even a second in the fight against the virus. "Today we are going through a delicate phase in which analyzing thousands of molecular swabs is a problem, that's why rapid tests can help us "

The quick test is a tampone rinofaringeo, just like the classic molecular buffer. "It is performed by swiping a kind of cotton swab on the nasal and pharyngeal mucosa, the swab is first mixed with a reagent and then analyzed on a solid support where the reaction is formed in a very short time, it is an almost immediate reaction".

When it is necessary to do an antigen or molecular test

The buffer (antigenic or molecular) is necessary, as written on the website of the Ministry of Health, when:

  • you have suspicious symptoms such as dry cough, sore throat, fever: in this case the general practitioner or pediatrician promptly requests the (free) diagnostic test;
  • there was a close contact with a person who tested positive.

First of all it is important contact your doctor or the pediatrician who will assess the situation and what to do on the basis of the information provided. If the doctor decides to prescribe a rapid antigen test or molecular test, it must be borne in mind that, in general, the positiveness will be found only a 48 / 72 hours away from contact with the virus positive subject. So it won't do any good to queue up for the swab the day after we come in contact with a positive because the outcome could be a false negative.

What to do if the antigen test is positive

If the antigen test is positive, a molecular buffer classic to confirm or not the diagnosis. If the molecular buffer is also positive, you have to stay in isolation for 10 days and thereafter repeat the test. In presence of symptoms, you need to wait until these have disappeared by at least 3 days before running the swab again.

How reliable is the negative unsanitary test

Dr. Clementi explains that "these tests were developed together with molecular tests, but initially they were discarded because they were not sensitive enough, but then they have been improved and now they have reached a good degree of sensitivity, around 90% more or less ".

As we have seen, the result is reliable if the test was performed at least 48/72 hours after contact. However, cases of false negatives, which is why it is always advisable to follow all hygiene rules provided to avoid contagion. In case of close contact and negative tampon, it is still necessary to stay in isolation for 10 days. 

When using rapid antigen tests

According to Dr. Clementi antigen tests can be useful in all those situations where speed is the most important element and when there is a need to have a result on a large number of subjects, as in airports, in workplaces, but also in schools.

Off to antigen tests in schools

Precisely because we know that even the children are prone to SARS-CoV-2 infection, although symptoms are usually mild, the Ministry of Health has decided to use antigen tests such as prevention tool in schools. On the website of the Ministry of Health we can in fact read: "The frequency of febrile episodes in the school population in the autumn and winter period will presumably be very high and it will be necessary to often resort to the practice of the swab to quickly exclude the possibility that it is COVID- 19 and to quickly identify cases, isolate them and trace their contacts ". If in fact it is true that Covid-19 affects children to a lesser extent, it is also true that it is still about infectious subjects. Through rapid antigenic tests it will therefore be easier to trace the positives, preventing the infection from spreading to peers, adults and the elderly, such as grandparents, who may be more at risk.

Read also: Covid-19, the Cts has given the okay to rapid tampons in schools

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