COVID-19 Saliva Tests Could Detect Silent Carriers

The scientists tested and compared the nasopharyngeal swabs and saliva samples of almost 2,000 people in Japan who did not have COVID-19 symptoms. Two different virus amplification tests were performed on most of the samples: the PCR test, which is now well-known and widely available around the world, and the less commonly used but faster and more portable RT-LAMP test.

The number of positive and negative results in all samples was very similar, with the nasopharyngeal swabs and saliva samples able to detect those with the infection in 77-93% and 83-97% of subjects, respectively. Both two tests were also able to identify those without the infection in greater than 99.9% of subjects. The virus loads detected in nasopharyngeal swab and saliva were equivalent and highly correlated.

“PCR sensitivity is much higher than previously thought 70% that came from initial data of symptomatic patients,” said Hokkaido University researcher Takanori Teshima, who led the study. While finding both nasopharyngeal and saliva samples have high sensitivity and specificity to the SARS-CoV-2, Teshima said “Saliva testing has significant logistic advantages over the commonly used nasopharyngeal swab testing.” “Self-collection of saliva is painless for examinees, and more importantly, it eliminates the close contact with the examiners, reducing the risk of viral exposure.”

“We also found that it is unlikely that the sensitivity of RT-LAMP is significantly less than that of the PCR test, suggesting that it might be a useful alternative for diagnosing COVID-19 infection, especially where diagnosis is required at the point of sample collection, like in sports venues or at airports,” added Teshima.

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Hokkaido University