Saliva tests could detect asymptomatic Covid-19 cases quickly, study says

Testing self-collected saliva samples could offer an easy, quick and effective mass testing approach for detecting asymptomatic Covid-19 cases, according to a study.

The research, published in the journal Clinical Infectious Diseases, tested and compared the nasopharyngeal swabs and saliva samples of almost 2,000 people in Japan who did not have Covid-19 symptoms.

"Rapid detection of asymptomatic infected individuals will be critical for preventing Covid-19 outbreaks within communities and hospitals," said Takanori Teshima from Hokkaido University in Japan.

Two different virus amplification tests were performed on most of the samples: the widely available PCR test, and the less commonly used but faster and more portable RT-LAMP test.

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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 per cent and 83-97 per cent of subjects, respectively.

Both the tests were also able to identify those without the infection in greater than 99.9 per cent of subjects, the researchers said.

The virus loads detected in nasopharyngeal swab and saliva were equivalent and highly correlated, they said.

"PCR sensitivity is much higher than previously thought 70 per cent that came from initial data of symptomatic patients," Teshima said.

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," said Teshima.

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"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," Teshima said.

Researchers point to a limitation of the study that they did not follow up with clinical outcomes.

They suggest that the results give good indication that mass screening using self-collected saliva and rapid RT-LAMP testing could provide easy, non-invasive, quick and relatively accurate results, with minimal risk of viral transmission to healthcare workers.