Saliva outperforms nasopharyngeal swabs for COVID-19 detection

Compared with nasopharyngeal swabs (NPS), saliva samples provide higher diagnostic yield for detecting positivity to the coronavirus disease 2019 (COVID-19), a recent study has found.

The researchers collected NPS-saliva sample pairs from 140 symptomatic patients with confirmed COVID-19. On the day of admission, 92.14 percent (n=129) of saliva samples tested positive for SARS-CoV-2 RNA, while the rest tested negative. At the same time point, only 52.63 percent of NPS samples were positive for the virus, while the rest were negative.

On day zero, saliva and NPS samples showed a 70-percent agreement for detecting COVID-19. McNemar’s test further showed that saliva samples yielded a significantly greater positivity rate than NPS samples (odds ratio, 6.64, 95 percent confidence interval [CI], 3.5–12.5; p<0.01).

On day 8, 77.42 percent of available saliva samples tested positive for viral RNA, as opposed to only 20.28 percent of NPS specimens. At this time point, the overall percent agreement between the two tests was 75.83 percent.

The higher positivity rate in saliva samples may have been driven by higher viral loads, according to the researchers. An analysis of 72 pairs of saliva and NPS samples showed that the former had significantly lower cycle threshold values than the latter, suggesting greater viral load (24.31 vs 32.66; p<0.001).

“Our data show that saliva has better diagnostic yield than NPS for diagnosis of SARS-CoV-2 infection,” the researchers said. “Taking these all into account, we recommend the use of saliva as good alternative to NPS sample in diagnosing COVID-19 patients.”