Faced with the risk of a new explosion of the Covid-19 epidemic, France is deploying in schools, from Monday February 22, a new screening tool. The Minister of Education, Jean-Michel Blanquer, announced on Saturday that“Between 50,000 and 80,000 tests” saliva would be achieved the first week, reaching 200,000 weekly.
The pupils of zone A (academies of Besançon, Bordeaux, Clermont-Ferrand, Dijon, Grenoble, Limoges, Lyon and Poitiers), who return to school on Monday, are the first to experience this device. Then come those in zones B (Aix-Marseille, Amiens, Caen, Lille, Nancy-Metz, Nantes, Nice, Orléans-Tours, Reims, Rennes, Rouen and Strasbourg) and C (Créteil, Montpellier, Paris, Toulouse and Versailles) , whose vacation ends, respectively, on 1is and March 8.
How do saliva tests work?
This is the least restrictive test. Unlike the nasopharyngeal swab – often painful when the swab is passed through the nose – the saliva test is not invasive, therefore particularly suitable for children. To take the sample, they will have to spit at least one millimeter of saliva into a vial. If the youngest, under the age of 6, fail to spit, saliva can be collected under the tongue using a pipette.
Accuracy of official website of the public service : sampling “Must be carried out 30 minutes after the last intake of drink, food, cigarette (or e-cigarette), tooth brushing or oral rinsing”. The sample, which must be analyzed within 24 hours of collection at the latest, can be stored in a dry, sterile bottle at room temperature. It must be returned to the analysis laboratory as quickly as possible.
This sample also has the advantage of not mobilizing a health professional to push the swab into the nostrils. “The saliva sample can be performed in an assisted manner or as a self-sample at the medical biology laboratory, at home or at a screening site”, details the site.
However, these are not rapid tests, like antigen tests. The turnaround time for results is similar to nasopharyngeal RT-PCR tests, approximately 24 hours. If the test is positive, a systematic search for a variant will be applied.
How reliable are they?
The extension of RT-PCR tests to saliva samples is based on a analysis carried out by a group of experts in epidemiology, infectiology, virology and methodology from the Haute Autorité de santé (HAS) on 4,520 pairs of positive tests (nasopharyngeal and salivary comparison). Since this study, a Covid-19 test has been deemed positive regardless of whether a positive response is obtained based on a nasopharyngeal or saliva swab.
However, it turns out that the saliva test is slightly less reliable than that performed in the nose. In his opinion delivered on January 22, the HAS had judged that the detections by RT-PCR on saliva should be judged reliable despite the loss of sensitivity of 3% to 13% compared to nasopharyngeal samples. That is to say a sensitivity of 85%, against 90% for nasopharyngeal samples. Sensitivity measures the ability of a test to detect as many infected people as possible, and therefore to generate as few false negatives as possible.
“This differential [de sensibilité] is to be weighed against the acceptability of the saliva sample, compared to the nasopharyngeal, for example in children or in populations for whom a test must be repeated regularly “, noted the opinion of the HAS.
What devices are recommended?
In an opinion issued on February 11, the HAS authorized the use of this method in the context of screening “On a large scale” on a closed group, such as schools, universities, nursing homes or nursing staff. The use of a saliva test is also recommended for the search for contact cases “When nasopharyngeal sampling is difficult or impossible”.
“We have decided to deploy it first in schools”, had explained, the same day, the Prime Minister, Jean Castex, in a school of the 13e arrondissement of Paris, where the AP-HP was conducting a pilot operation. Setting a goal of at least 200,000 tests per week initially, Jean Castex had also mentioned their interest in caregivers, “Populations who are forced to test themselves often”.
How will this protocol be applied in schools?
These samples, which currently concern pupils in zone A, are not compulsory. They can be carried out after written agreement from the parents. They primarily concern kindergarten and primary school students, who are more sensitive to the nasopharyngeal test.
School staff also fear logistical difficulties for their implementation. “All the tracing is already on us because the regional health agencies and Social Security are overwhelmed”, says Saphia Guereschi, general secretary of Snics-FSU, the national education nurses’ union.
Liberal nurses and civil security can be mobilized to screen in schools, a recourse “Unequal” according to academies, according to the Snics-FSU. School doctors, for their part, warn of their inability to carry out large-scale saliva tests, particularly in departments where there are many students and school medicine too rare.
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