3. Lingual swab
The lingual swab (LS) or oral cavity swab (OCS) for detection of
SARS-CoV-2 involves swabbing the anterior two-thirds of the tongue or
the oral tongue. A Wuhan study compared LS with OPS and found that in 91
patients, the positive rate of OPS was higher than that of LS. However,
the authors noted that this difference may have been attributable to a
single experienced nurse collecting all of the
samples.11
Azzi et al reported the use of OCS and “oral saliva pipette
collection” for viral detection. In a cohort of 25 severe to very
severe COVID-19 patients (severity not otherwise specified but all
patients were mechanically ventilated in intensive care unit), it was
reported that SARS-CoV-2 was detected in all 25 patients’ salivary
swabs, with different Ct values (range 18.12 – 32.23, mean value 27.16
+/- 3.07). All patients had prior positive nasopharyngeal swabs at point
of diagnosis.12 The authors thus concluded that the
oral cavity saliva collection was a reliable method of viral detection.
It should be noted, however, that these results were from critically-ill
patients whose viral shedding patterns may be different from suspect
cases. Hence, the utility of oral cavity salivary swabs or LS may not be
reproducible in screening scenarios. Although the LS or OCS is simple
and presumably causes less discomfort, its use in the current pandemic
is unlikely to be prevalent due to the need to maximize sites sampling
and secretions collection to accurately diagnose infection.