Nasopharyngeal and Oropharyngeal Swabs Detect More COVID-19 Cases than Saliva Testing in New Study

A new study by Canadian researchers has found that nasopharyngeal and oropharyngeal swabs can detect more COVID-19 cases than saliva testing.

The team conducted the study to determine the detection rate of SARS-CoV-2 using a novel, self-administered kit for saliva collection compared with standard swab testing. The researchers prospectively enrolled consecutive, asymptomatic, high-risk persons and those with mild symptoms suggestive of COVID-19. Out of the 1,939 paired swab and saliva samples analyzed, SARS-CoV-2 E gene was detected in 70 samples, 80.0% with swabs and 68.6% with saliva. A total of 34 participants (48.6%) tested positive for SARS-CoV-2 on both swab and saliva samples. Discordant test results were seen in 22 participants (31.4%) who tested positive with swab alone and in 14 (20%) who tested positive with saliva alone. Swabs were obtained from the nasopharynx in 35.7% of participants who tested positive with saliva alone, compared with 9.1% of participants who tested positive with swab alone.

Thus, the researchers found that standard diagnostic methods of nasopharyngeal and oropharyngeal swabs detected more COVID-19 cases than saliva testing among patients who were asymptomatic but at high risk or who were mildly symptomatic. The findings add to those of previous studies, which have focused on salivary tests of symptomatic or hospitalized patients and found that saliva tests may be more sensitive.

Due to RNA instability, the use of raw saliva necessitates rapid transportation to a laboratory for extraction of viral material and polymerase chain reaction analysis. The study was unique in that it used a novel collection kit containing a preservative and viricidal fluid, allowing for safe and stable storage and transport of the samples. The study showed the feasibility of a simple, safe collection tool for salivary detection of SARS-CoV-2 in the setting of a COVID-19 testing center. The researchers concluded that despite a lower estimated rate of detection relative to swab testing, saliva testing may be of particular benefit for remote, vulnerable, or challenging populations.