Saliva tests potential solution for asymptomatic carriers

Testing self-collected saliva samples could offer an easy and effective mass testing approach for detecting asymptomatic novel coronavirus (COVID-19), according to new findings by Hokkaido University published in the journal Clinical Infectious Diseases.

For the study, researchers 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 well-known and widely available polymerase chain reaction (PCR) test and the less common 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 percent and 83-97 percent of subjects, respectively. Both two tests were also able to identify those without the infection in greater than 99.9 percent of subjects. The virus loads detected in nasopharyngeal swab and saliva were equivalent and highly correlated, the researchers said.

While finding both nasopharyngeal and saliva samples have high sensitivity and specificity to the SARS-CoV-2, the researchers said saliva testing has significant logistic advantages over the commonly used nasopharyngeal swab testing. For example, self-collection of saliva is painless for examinees and eliminates the close contact with the examiners, reducing the risk of viral exposure. Additionally, the researchers said 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.

Many of the world's governments are showing reluctance to re-institute full national lockdowns as second waves of COVID-19 infections loom on the horizon. Testing and tracing systems will need to be ramped up to detect and isolate people who have the virus as early as possible, the researchers said.

"Rapid detection of asymptomatic infected individuals will be critical for preventing COVID-19 outbreaks within communities and hospitals," said Takanori Teshima, MD, PhD, lead author of the study, in a statement.

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