Health PCR test: if the saliva is contagious, why should...

PCR test: if the saliva is contagious, why should it be taken from the back of the nose? – CAMEROON MAGAZINE – CAMEROON INFO


There are several tests for coronavirus. But one of them questions internet users in particular: the PCR test, which consists of removing cells from the back of the nose. Internet users are wondering if it is really necessary to go to the bottom of the nose to detect the virus, when a simple drop of saliva, which is contagious, can be collected more easily.

Since the start of the coronavirus epidemic and all the more in recent days, comments relating to screening tests, in particular the PCR test, have flourished on social networks: “The coronavirus screening test worries me so much, I’ve never been so scared in my whole life, nothing will enter my nose “,” Does the coronavirus test (cotton swab in the nose) really hurt? “

The virological test or PCR consists in looking for the Sars-CoV-2 virus in the secretions. This is done using a cell swab from the bottom of the nose. The samples are then analyzed with the PCR (polymerase chain reaction) technique by a specialized laboratory to identify the presence of the virus in the secretions. This type of test arouses the fear of Internet users because it can be unpleasant or even painful.

An image of this test, known as “transnasal”, has recently circulated on social networks. It is accompanied by a suspicious legend: “I wonder why they stick a Q-Tip in the nose to the back of the head to collect a sample of Covid-19, when they claim that a simple drop of saliva has the potential to infect an entire village? “

This interrogation attests to a misunderstanding of the operation and transmission of the Covid-19. The virus is present both in the respiratory tract and in saliva. However, it does not circulate in the same way in these two areas and is not transmitted primarily by drops of saliva.

“Saliva is not a good transport medium for the virus, which prefers the cells of the respiratory tree. Transmission is mainly through the water vapor present in respiration, “explains to the world Laurent Andreoletti, professor of virology at the Faculty of Medicine of Reims and head of a Covid-19 diagnostic unit. This is why wearing a mask is recommended.

Although it can be scary, the PCR test is the most reliable. According to the professor, its reliability is around 80 to 90% if it is well done, against 60 to 70% for a saliva test. “Even though the virus can be found in saliva and the throat, it is more present in the hair cells of the respiratory tree. This limits the percentage of false negatives, ”says Laurent Andreoletti.

A sample from the back of the nose is also necessary because the virus first lodges in the respiratory tract. It is in this area that it is possible to identify it early. “We don’t know exactly when it comes in saliva; when we know that we will find it in the mucous membranes, which are the place of primary infection ”, specifies to the World Bernard Binetruy, Inserm research director, in charge of scientific communication in charge of PCR tests. “If we were only doing saliva tests, we would be missing out on people who have the virus and are in the early stages of infection but would not yet be detectable,” he continues.

The PCR or virological test is not the only one allowing the detection of Covid-19. There is also the serological test, which is carried out using a blood sample. The latter makes it possible to examine the serum and aims to seek the antibodies produced by the body to fight against the virus. Another way to spot the Covid-19: the quick test. This identifies the presence of antibodies in the body using a drop of blood. Lesser known saliva tests also help to know if the person being tested is carrying the virus at the time of sampling.

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