A self-test before homework. Thanks to the relaxation of the health protocol in schools, self-testing for Covid-19 has burst into the lives of many French people. In order not to close too many classes in the face of the wave of contamination linked to the Omicron variant, parents were thus invited to have their child contact case undergo three self-tests, without the obligation of antigen or PCR testing. Their offspring can then continue to go to class, after bringing back a negative test sworn statement.
Introducing a swab into a child’s nose is not necessarily easy, however. To make the task less difficult, some parents explain on social networks that they use self-tests to take samples from the mouths of the youngest. Is right ? Response elements.
Taking a sample from the mouth rather than the nose is nothing new. The practice has even been fully accepted since an opinion published by the High Authority for Health (HAS) at the end of September 2020. The HAS pointed out at the time that people for whom nasopharyngeal sampling was contraindicated could be offered a saliva sample, or, for asymptomatic patients, an oropharyngeal (throat) swab.
“In the laboratory, we first offer the classic nasopharyngeal sample. If the patient sees this as an inconvenience, or if it is impossible (for example after a nose operation), we can proceed to a saliva sample. Finally, in third intention, we can take a so-called oropharyngeal sample, during which we will take the sample from the back of the throat, as we would do for the search for angina “confirms to franceinfo François Blanchecotte, president of the Syndicate of biologists.
However, these alternative screening methods are reserved for a single type of analysis: PCR tests. “This type of sample is not suitable for self-tests or current antigenic tests”, explains Jean-Claude Azoulay, president of the National Syndicate of Medical Biologists. These screenings only show a positive result if the quantity of virus in the sampled material reaches a certain level, where a PCR analysis amplifies the content of the sample to detect traces of virus, even in small quantities.
“Today, these salivary or oral samples can only be revealed with a PCR test, which have greater sensitivity and will not miss a rare presence of the virus.”
Jean-Claude Azoulay, President of the National Syndicate of Medical Biologistsat franceinfo
“The High Authority for Health has confirmed the good sensitivity of saliva RT-PCR tests. The sensitivity of these tests is estimated at 85%, which is slightly lower (3% to 11%) than that of RT-PCR tests, which use the nasopharyngeal swab”, underlines for its part the General Directorate of Health. She adds on her website that “self-tests and antigenic tests on saliva samples are not authorized in France by the HAS because of their performance deemed insufficient”.
The risk of missing a positive case is particularly high if the patient is asymptomatic. “Self-tests and antigenic tests are by default less sensitive, and if in addition the patient is carrying less virus than a highly symptomatic person, you will have fewer possibilities of detecting it”explains François Blanchecotte.
However, the doctrine could evolve with the Omicron variant. A study published at the end of December by South African researchers (article in English) argues that a salivary PCR test would be 100% effective in detecting Omicron, compared to 86% for a simple nasal PCR (and not nasopharyngeal, for which the sample is deeper). Results that “suggest higher viral shedding in saliva compared to nose with Omicron”write the authors.
This study, which has not yet been peer-reviewed, has the additional disadvantage of having tested saliva sampling with a very strict protocol, reports The Parisian, which echoed it in mid-January. Participants had to refrain from eating, drinking or smoking for 30 minutes before the test, then cough at least three times, before passing a swab inside both cheeks, on the tongue, gums and the palate for at least 30 seconds. “A procedure probably less painful than going deep into the nostrils, but not obvious in practice”wrote the daily.
These results are however in line with an overall easier observation of this variant. “Omicron is very present everywhere: in saliva, as in nasopharyngeal samples”confirms Jean-Claude Azoulay, who ensures that the production of more reliable salivary antigen tests is “on the right track”.
Contacted by The Parisianthe HAS indicated in mid-January “study new data on the effectiveness of different types of tests against Omicron”, and in particular antigenics and saliva self-tests. According to his observations, parents could soon avoid crying spells when it comes time for the now unavoidable test.