For the green pass and in the context of monitoring the circulation of the virus in schools and other limited contexts, molecular salivary tests are recognized as valid. However, rapid antigenic salivary tests cannot be used for the green card issue, and this is due to the insufficient level of precision found in all the studies. According to the new indications provided in a new circular from the Ministry of Health, the molecular test on nasopharyngeal and oropharyngeal respiratory sample “still remains the international gold standard for the diagnosis of Covid-19 in terms of sensitivity and specificity”.
How the tests work
Traces of the virus can be detected directly from saliva in two different ways. One detects the genetic material of the virus (ie the presence of the RNA in the sample) and is based on a particular analysis (polymerase chain reaction) that can only be carried out in the laboratory. Salivary antigenic tests, on the other hand, provide a result within about ten minutes by identifying the surface proteins of the SARS-CoV-2 virus present in saliva.
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All the advantages
The role of saliva as an alternative sample type has been a focus of study since the beginning of the pandemic, due to the practical difficulties of collecting nasopharyngeal and oropharyngeal swabs. In a summary technical report last May, the ECDC, the European center for disease control, admits that saliva sampling can contribute to the timely identification of infected individuals in the community by lining up all the benefits. Saliva is an easy-to-collect, non-invasive, and well-accepted sample collection method by both healthcare and non-healthcare professionals, as well as ordinary people. It generally does not require special equipment for collection, so it can lead to a reduction in the resources required (laboratory and personnel resources, personal protective equipment, etc.) Furthermore, self-collection of the sample is possible, also reducing the risk of exposure of health professionals.
The limits of use
However, according to the expert panel, the results of the studies are variable and often showed that the detection sensitivity of viral RNA in saliva was lower than that of nasopharyngeal or oropharyngeal swabs performed on the same day as salivary collection from the same patient, even though some studies have even shown slightly higher sensitivity of saliva samples. However, during the period of maximum viral load, the sensitivity is comparable and sufficient to reliably detect infected individuals. Saliva-based RT-PCR tests best perform during the first five days onset of symptoms and when viral load is high. With the problem that the composition of saliva samples can be heterogeneous and therefore further studies are needed to evaluate the performance and standardize the various methods of saliva collection. The evidence therefore supports the conclusion that saliva can be used as an alternative sample for RT-PCR tests, when nasopharyngeal swabs cannot be collected as in the particular case of symptomatic patients and for repeated screening of asymptomatic individuals. When it comes to antigen tests, however, the reserves of the specialists involved in the ECDC report increase, in light of the very few clinical validation studies on the use of saliva as sample material for rapid antigen tests and not enough data available on the test sensitivity.
Sensitivity between 53 and 73% was detected in pediatric age
“Since saliva collection is easy and non-invasive, it should offer a feasible approach for widespread SARS-CoV-2 testing in children. Unfortunately, data on the use of saliva to detect SARS-CoV-2 in pediatric patients is scarce. ” The few reports available on saliva sample performance for children showed poor detection of SARS-CoV-2, with sensitivity ranging from 53 to 73%, not counting the small sample size. In a study published in February 2021, the authors concluded that saliva is a reliable diagnostic sample for detecting SARS-CoV-2 RNA by RT-PCR, particularly for symptomatic and asymptomatic children and symptomatic adults.