Introduction
Diagnosis of Severe Acute Respiratory Coranavirus-2 (SARS-CoV-2) infection is currently based on Real-Time PCR (RT-PCR) performed on either nasopharyngeal (NPS) or oropharyngeal (OPS) swabs;1 however, it has been described that a negative NPS or OPS does not rule out coronavirus 2019 (COVID-19), and this could be related to different situations.2 Given the fact that SARS-CoV-2 RNA title in the upper respiratory tract peaks between days 7-10 after the clinical onset, a late sample timing could account for a false negative result.2
It is well known that diagnostic accuracy of NPS and OPS is not so high, being the detection rate of SARS-CoV-2 RNA respectively of 63% and 32%;1 therefore, UNITED States Centers for Disease Control and Prevention have recommended the collection of sole upper respiratory NPS.1 Reduced detection rate could be related to either inadequacy of sample collection into the nasopharynx (the risk that the collection of secretion is performed into the nasal cavity rather than the nasopharynx is not neglectable, given the incomplete patient cooperation during this unpleasant manoeuvre),3 or a limited viral local tropism due to the low expression of ACE-2 receptors in the epithelial cells of the nasopharyngeal/oropharyngeal surface.
Despite these considerations, collection of upper airway secretions by means of NPS/OPS still represents the first line diagnostic modality to test patients and otherwise asymptomatic population for COVID-19, provided that it is early and adequately performed after onset of symptoms. Self-collection of saliva samples has been proved to be an alternative safe, cheap and non-invasive diagnostic mean to confirm SARS-CoV-2 infection.4,5