Also salivary tests join the tools we have at our disposal in terms of screening and of monitoring of Sars-CoV-2 infection. The Ministry of Health gave the green light to these less invasive examinations of the oral-nasopharyngeal swabs (regardless of whether their analysis is then molecular or searches for the antigen), which will be extremely useful in the context of reopening in different scenarios, from weddings over a certain number of school guests to events with a large number of people.
This is with regard to generic and control screening to obtain the “green pass” useful for moving around or, in fact, for accessing certain events. In terms of identifying the infection, that is, when the swab is done why they accuse themselves of the symptoms, the director general of Prevention Gianni Rezza writes in the new circular that “sensitivity decreases after the first 5 days onset of symptoms»And therefore that kind of test must be used within that deadline from the beginning of fever, cough, exhaustion and all the other symptoms we know, connected to Covid-19. In any case, “the saliva sample can be considered an option for the detection of Sars-CoV-2 infection if it is not possible to obtain gold / nasopharyngeal swabs”. Because the highest standard remains the real time RT-PCR test. In short, the molecular we have known since the beginning of the emergency.
Therefore the saliva sample “can be considered an option for the detection of Sars-CoV-2 infection in asymptomatic individuals repeatedly screened for professional or other reasons, to increase theacceptability of repeated tests, in particular: if very elderly or disabled individuals are screened and if there is a shortage of tampons ». However, it is very likely that this indication can also extend to the situations indicated above, where there is no need to investigate symptoms and where guests or participants are obviously asymptomatic.
But be careful: the collection of the saliva sample, although less invasive, however, it must be done correctly. “The saliva samples can be heterogeneous (oral saliva, posterior oropharyngeal saliva) and the different techniques and collection sites can have an impact on the sensitivity of the method – adds the circular – moreover the saliva samples can be mucous and viscous, causing difficulties processing with existing automated RNA extraction or extraction / amplification methods and equipment ‘. This is because in that sample the genetic code of the coronavirus will be searched for, therefore a molecular type analysis.
But the saliva was evaluated “as a possible substrate for antigen tests based on automatic laboratory instrumentation, with chemiluminescence reading – concludes the circular – at the moment, the available repertoire of such Ce-Ivd labeled tests for the salivary matrix is ​​limited, but is being expanded. The comparison with the molecular test indicates for the saliva a sensitivity similar to that observed for the nasopharyngeal swab ». In short, the salivary sample will soon be suitable for laboratory or rapid antigenic analysis.
It should be remembered that the sensitivity of a test corresponds to the ability to correctly identify infected subjects. Therefore, if a test has excellent sensitivity, the risk of false negatives is low. There specificity it is instead the ability to keep the rate of false positives very low. This sensitivity, for the salivary sample, decreases after the first five days of symptoms: this is why they should be used for diagnostic purposes at the beginning of the problems. In the other cases, however (obtain green certification to move between orange and red regions and to participate in events) it will essentially be just a local and national political choice.
Molecular saliva tests “may represent a useful tool for monitoring and controlling Sars-CoV-2 infection in school environment. Some studies published in 2020 have found sensitivities ranging between 53 and 73% »reads the ministerial decision. They could already be used for eighth grade exams, which will begin at the end of the lessons, and of maturity, starting June 16. The count of these tests will end up, as for the others, in the regional surveillance systems and therefore will in all probability be indicated and counted in the daily bulletin, with all the consequences of the case on the positivity rate.
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