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Japan: Covid-19 Detection Saliva Tests Could Detect Silent Covid-19 Carriers

| Editor: Alexander Stark

Scientists at Hokkaido University and colleagues in Japan have demonstrated a quick and effective mass testing approach using saliva samples to detect individuals who have been infected with Covid-19 but are still not showing symptoms.

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Japanese scientists have demonstrated a quick and effective mass testing approach using saliva samples.
Japanese scientists have demonstrated a quick and effective mass testing approach using saliva samples.
(Source: Public Domain / Pixabay )

Hokkaido/Japan — 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 in order to detect and isolate people who have the virus as early as possible.

Rapid detection of asymptomatic infected individuals will be critical for preventing Covid-19 outbreaks within communities and hospitals. Testing self-collected saliva samples could offer an easy and effective mass testing approach for detecting asymptomatic Covid-19.

In a study, Hokkaido University researcher Takanori Teshima and colleagues 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. Teshima says that PCR sensitivity was much higher than previously thought 70 % that came from initial data of symptomatic patients.

Both nasopharyngeal swab (NPS) and saliva testing showed high sensitivity and specificity to the Sars-Cov-2.
Both nasopharyngeal swab (NPS) and saliva testing showed high sensitivity and specificity to the Sars-Cov-2.
(Source: Yokota I et al., Clinical Infectious Diseases)

While finding both nasopharyngeal and saliva samples have high sensitivity and specificity to the Sars-Cov-2, Teshima stated that saliva testing had significant logistic advantages over the commonly used nasopharyngeal swab testing. Self-collection of saliva was painless for examinees, and more importantly, it eliminated the close contact with the examiners, reducing the risk of viral exposure, he argues. “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,” says Teshima.

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

Original article: Isao Yokota et al., Mass screening of asymptomatic persons for SARS-CoV-2 using saliva. Clinical Infectious Diseases, September 25, 2020. DOI: 10.1093/cid/ciaa1388

(ID:46896180)