Saliva Tests Show Promise 🤞
Data suggests spit may be an acceptable alternative to nasopharyngeal swab samples to detect Covid-19
I need to disclose some bias. I would much prefer to spit in a tube than have a swab spun around in the back of my nose and throat. To be clear, I’ve happily received multiple nasopharyngeal swabs because it’s important to get tested for Covid-19. While I don’t actually think the nasopharyngeal swab is painful (though others disagree), I do find it uncomfortable, and I’ve been keeping my fingers crossed for more widespread use of tests that rely on saliva.
Now there’s some early research published in the New England Journal of Medicine that offers strong support for using saliva as an alternative to nasopharyngeal swab samples to detect SARS-CoV-2, the virus that causes Covid-19.
The researchers at Yale School of Public Health and the Yale School of Medicine studied 70 people with confirmed Covid-19. The men and women first tested positive for Covid-19 with the standard nasopharyngeal swab, and also agreed to provide saliva samples that they collected themselves. The researchers tested both samples and detected more SARS-CoV-2 RNA copies in the saliva samples than in the nasopharyngeal swab samples. A higher percentage of saliva samples than nasopharyngeal swab samples also tested positive up to 10 days after the Covid-19 diagnosis. The researchers also observed less variation in levels of SARS-CoV-2 RNA in the saliva samples. “These findings suggest that saliva specimens and nasopharyngeal swab specimens have at least similar sensitivity in the detection of SARS-CoV-2 during the course of hospitalization,” the researchers write.
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The researchers also looked at the effectiveness of using saliva samples to identify the virus in people without symptoms of Covid-19. They screened nearly 500 asymptomatic health care workers and tested both saliva and nasopharyngeal samples from the men and women. They found SARS-CoV-2 in the saliva samples of 13 people who did not have any symptoms when the samples were collected. Among those 13 health workers, nine had nasopharyngeal swab samples collected that day and seven of those samples tested negative. “The diagnosis in the 13 health care workers with positive saliva specimens was later confirmed in diagnostic testing of additional nasopharyngeal samples by a CLIA (Clinical Laboratory Improvement Amendments of 1988)-certified laboratory,” the researchers report.
The researchers reason that some of the differences in results seen in the saliva samples versus the nasopharyngeal swab samples in the health care workers has to do with the fact that the health workers gave themselves the nasopharyngeal swabs, and there could be more variation in how those samples were collected.
“Collection of saliva samples by patients themselves negates the need for direct interaction between health care workers and patients,” the researchers write. “This interaction is a source of major testing bottlenecks and presents a risk of nosocomial infection.”
The study findings imply that spit is a pretty good sample for finding Covid-19, and that people’s ability to collect saliva samples from themselves not only cuts down on personnel needs, but also supplies for swabs and personal protective equipment. “Given the growing need for testing, our findings provide support for the potential of saliva specimens in the diagnosis of SARS-CoV-2 infection,” they conclude.
While the study is well done and provides strong support for using saliva in Covid-19 testing, it’s still relatively small, and so more research may be needed. Even so, there’s already a push among scientists for more widespread embrace of rapid-responding Covid-19 tests that use saliva, since that’s an easier testing strategy for people to embrace in their homes. Sign me up!