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