First NZ study to diagnostically validate COVID-19 saliva testing

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Scientists at Te Herenga Waka—Victoria University of Wellington have used real-world samples to confirm the 98.7 percent accuracy of a saliva test for COVID-19. This is the first, and currently the only, COVID-19 saliva test to be diagnostically validated in Aotearoa New Zealand.

Associate Professor Janet Pitman from the University’s Te Kura Mātauranga Koiora—School of Biological Sciences led the study. “Despite a view that saliva tests aren’t as accurate as the standard nasopharyngeal test, our research shows this one is,” she says. A paper describing the study has been prepared and submitted for publication in a medical journal.

Initial testing was carried out on artificially infected saliva, where heat-inactivated SARS-CoV-2 virus, which causes COVID-19, was added to saliva in the lab. The now-completed diagnostic validation involved testing samples from actual positive COVID-19 patients.

Associate Professor Pitman’s team tested paired samples, sent from the United States, from 152 people. The paired samples were a sample of saliva and a sample from a nasal swab taken at the same time. Thirty-four of these people were positive for COVID-19.

In all but two instances, the results matched—in one instance the saliva sample tested positive when the nasopharyngeal sample didn’t, and in the other the reverse occurred. The discordance between the two samples is likely not due to a failing of either test. It is more likely due to differences in the timing of the virus’s presence during the early stages, and disappearance during the late stages, of the disease at the two biological sites (salivary glands and the nasopharyngeal region). Salivary glands contain large numbers of cells that replicate the virus and are then shed into the saliva, making saliva a great indicator of live virus production.

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