How the salivary test for coronavirus works

Green light from the Ministry of Health to use salivary tests to detect the coronavirus, but the gold standard remains molecular swabs

(image: Pixabay) The Ministry of Health, in a circular signed by the director general of Health prevention Gianni Rezza, said yes to saliva tests to track down the coronavirus. In light of the latest scientific evidence, experts believe that the less invasive salivary tests are sufficiently reliable, and therefore usable in precise situations: in case there is no possibility of performing a nasopharyngeal or oropharyngeal swab (which remains the gold standard) or in in case of need for repeated tests or on children, the elderly and the disabled. Here's how they work, advantages and limitations.

The available tests

First you need to clarify what kind of test you are talking about. At the moment, molecular tests can be performed on saliva, that is, they search for the viral genome (rna), or laboratory antigenic tests (that is, they search for virus proteins), but, in short, they are not rapid tests. In fact, there are also rapid antigenic tests on saliva, which however have not yet been included in the list of the Health Security Committee of the European Union.

"At present, the available repertoire of such CE-IVD marked tests for the salivary matrix it is limited, but it is in the process of enlargement ”.

Sample collection

Saliva sample tests are less invasive than swabs. However, the correct collection of the material is crucial, the ministry experts write. “Saliva samples can be heterogeneous (oral saliva, posterior oropharyngeal saliva) and different techniques and collection sites can have an impact on the sensitivity of the method. In addition, saliva samples can be mucous and viscous, causing difficulties in processing with existing automated RNA extraction or extraction / amplification methods and equipment ".

Sensitivity

sample quality and collection technique can influence the sensitivity of the test, which is therefore variable. "A greater sensitivity was detected in the posterior oropharyngeal saliva in the early morning", reads the ministerial circular, "while a lower sensitivity was observed with the 'general spitting' technique (spitting, ed)".

Who can do the salivary test

For the moment salivary tests can be used when there is no tampon available, or in children (data in pediatric age are limited but some studies attest to the sensitivity of the test between 53 and 73%), elderly and disabled, or in contexts of repeated screening for professional reasons. They may find ample scope for use in schools.

The saliva sample test can be performed both on symptomatic people (preferably within the first 5 days of the onset of symptoms) and on asymptomatic or pre-symptomatic people.


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