The Minister of Health announced the use of saliva tests in schools after the February recess. How effective are they in screening for Covid-19? Are they fast? Answers with Professor Jacques Izopet, head of the virology service at Toulouse University Hospital, who published a study this summer.
Less invasive, easier to use and less exposing the staff taking the sample to the virus, the saliva test appears to be much more attractive than the nasopharyngeal swab to detect Covid-19. But is it also efficient? While waiting for the position of the Haute Autorité de Santé (HAS), we put the question to Professor Jacques Izopet. Its virology laboratory (Toulouse University Hospital) published a study on the subject this summer (1). Another will soon be submitted for publication.
“According to our work, carried out during the first quarter of 2020, saliva tests appear to us to be as effective as nasopharyngeal samples”, launches the virologist. The Toulouse laboratory compared the sensitivities of saliva samples and nasopharyngeal swab samples to detect SARS-CoV-2, the coronavirus that causes Covid-19, in 123 people. The virus detection technique was done by RT-PCR as for current screening tests, in the laboratory. The results were obtained after several hours according to the well-established laboratory protocol of RT-PCR, and not in 40 minutes like the commercial saliva test from the Montpellier firm EasyCov.
A concordance rate of 85%
The saliva samples from the Toulouse study detected 82.2% of Covid-19 positive patients against 93.2% for nasopharyngeal samples. The agreement rate for the two methods is around 85%. “It is possible to have a negative nasopharyngeal sample and a positive saliva sample and conversely to have a positive nasopharyngeal sample but negative at the salivary level. When the viral load is low, the same technique can give positive and negative results “, relates Professor Jacques Izopet for whom this 85% agreement validates the technique of detection by RT-PCR of saliva samples, which” have above all the advantage of being less invasive than nasopharyngeal swabs ”.
For asymptomatic people, the Toulouse study shows poorer results of saliva tests, “probably due to a lower viral load, as can be found in nasopharyngeal tests”.
“Interesting for large-scale screening in the population”
In conclusion, “saliva tests could be of interest for large-scale screening, for example in universities or during mass operations as there were in the cities of Roubaix or Saint-Etienne. We can legitimately assume that they will generate more support from the population. », Slips the virologist.
As with nasopharyngeal swabs, saliva samples (obtained from sputum) would then be sent to public and private laboratories, now equipped and experienced in performing mass analyzes. “To treat a more limited number of people, for example in an airport or a school, the EasyCov type solution would be interesting. We are going to move towards additional proposals, such as when antigenic tests supplemented the RT-PCR technique, ”adds Professor Jacques Izopet.
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