Molecular and antigenic salivary tests: differences and validity for green pass

From 19 September i molecular salivary tests (those tested in the laboratory, not the rapid antigens) can be used for the issue of the green pass. The law 126/2021, the first green pass decree of 6 August, published in the Official Gazette on the 19th of the month.

A circular of the Ministry of Health returns, once and for all, to take stock of the use of a sample saliva in place of the oropharyngeal swab. Specifying some elements both on the samples processed with molecular analysis and on those, also possible, rapid antigenic (which, we remember, they do not give the right to issue the digital green certificate).

In the first case, the document, signed by Giovanni Rezza, director of the general department of prevention, recalls that “recent scientific evidence on molecular salivary tests have identified sensitivity values ​​between 77% and 93%. school reported a high agreement between the results obtained with salivary molecular test and with molecular test on nasopharyngeal and oropharyngeal sample ». In short, the salivaries work. However, the classic swab (with sampling from the nose and throat) “still remains the international gold standard for the diagnosis of Covid-19 in terms of sensitivity and specificity”.

While they work, the use of this type of test should be limited to specific situations. This because “it requires a higher number of steps which lead to longer sample processing times“. For this reason, precisely in order not to overload the regional microbiology laboratories (which in addition to the ordinary activities are involved in monitoring the circulation of Sars-CoV-2 in the school environment) “molecular tests on salivary samples, at least in the initial start-up phase , may be considered an alternative option to gold / nasopharyngeal swabs only “in some cases. Which ones are they? Symptomatic or not fragile individuals and with poor collaboration skills, screening of children in the school monitoring plan or in any case in general in the educational field, health and social health workers in the context of scheduled screening in the workplace. People, in short, who have to do so many and frequently with tampons. Everyone else should continue to use oropharyngeal rapid molecular or antigenic tests. The ones we have been doing since the beginning of the pandemic.

Among other things, the collection of the salivary sample (which the circular calls matrix) is a crucial step and can strongly influence the sensitivity of the test. For this reason “the ministry therefore recommends careful observance of the indications provided by the manufacturers of the collection device used”. In any case, if the molecular salivary were to declare a positivity, an oropharyngeal confirmation swab will not be required.

So far we have talked about molecular salivary swabs, the only ones that give right to the green pass. For those antigenici, however, the matter changes completely: “The rapid antigenic tests on saliva, on the basis of the available evidence, they are not recommended at the moment as an alternative to gold / nasopharyngeal swabs, as they do not reach the minimum acceptable levels of sensitivity and specificity“Explains, without compromise, the ministry, who remembers precisely how” the antigenic tests on salivary matrix are currently excluded from the common European list of rapid antigen tests valid to obtain the Covid-19 green certification ». Something could change, given that “some scientific evidence is emerging regarding the possible use of salivary antigen tests based on measurement with laboratory instruments, which however are still being evaluated for the aforementioned applications”. We will see.

Finally, the document specifies that, as part of the monitoring plan and if the kit distributed allows it, the withdrawals from students can be made even at home by parents and guardians, “Following a preventive training process to achieve the necessary confidence with the collection devices”. Finally, but this should be taken for granted, the ministry reiterates that the results of molecular tests on salivary samples, including those performed in the context of screening activities, will have to be reported in the Covid-19 Surveillance System of both the ISS and the ministry.