A nucleic acid test through saliva collection?

The Ministry of Health, Labour and Welfare (MHP) has decided to novel Coronavirus nucleic acid test using saliva as a sample starting June 2, following a nasal swab sample previously used in Japan.
What are the benefits of a saliva sample?
How accurate is the nucleic acid test using saliva?
Jiefang Daily and Shangguan News reporter interviewed Professor LAN Ke, director of the State Key Laboratory of Virology, Wuhan University.

“Although the nucleic acid test works the same way, it is safer and easier to take a saliva sample than a nose swab.”
Ronker said.
Nasal swabs are taken by professionals, such as doctors, and patients who cough or sneeze at the time of collection are at increased risk of infection in the person collecting them.
To prevent infection, collectors are generally required to be “fully armed” for protection.
According to NHK, patients will be able to hand over bottles of their own saliva to their doctors, in an effort to reduce the risk of infection among health care workers, tackle understaffed and overburdened health care facilities and eventually expand testing coverage.

Similarly, in early May, FDA of the United States gave an urgent approval to use a saliva sample from a novel Coronavirus test in order to “increase the chance of testing a coronavirus from a novel”.

“It is important to note that saliva samples, although safer and easier to use, may only be detected in patients with high viral loads.”
Covid-19 is an acute respiratory infection, and the novel Coronavirus in the mouth has less viral load than the nasopharynx, Says Lankow.
That’s why hospitals in Japan warn patients not to brush their teeth or eat before collecting saliva, because the viral load in the mouth is not high enough. After brushing or eating, there is less virus and the test is not effective.

The results of a saliva test on hospitalized patients show the method is more accurate for patients within nine days of onset of illness, the Health ministry said.
Therefore, the ministry of Health, Labour and Welfare has decided to target saliva tests for patients within nine days of onset.

“It is very difficult to define how to determine the first 9 days after onset.”
In order to expand the scope of the test in a short time, Lanko believes that saliva test could be used as an auxiliary test.

Once a positive nucleic acid test is confirmed, he said, it is considered the “gold standard” and the most suitable method for mass screening.
“At present, the scientific research to improve the speed of nucleic acid detection is very encouraging, but accuracy should be the first goal.”

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