Saliva also has trade-offs. Although the virus appears to accumulate in saliva early on, the nose may be the best place to find it in the later stages of an infection.
Caltech researchers have found that while the virus often first appears in saliva, it eventually reaches higher levels in the nose. Their results show that highly sensitive tests, such as PCR tests, can detect infections in saliva days earlier than in nasal swabs, but less sensitive tests, such as antigen tests, may not.
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Some experts point out that data on saliva is still mixed.
“These few studies seemed really interesting to me,” said Dr. Mary C. Hayden, an infectious disease physician and clinical microbiologist at Rush University Medical Center in Chicago.
But Dr. Hayden said she is interpreting the new research with caution because “for years and years” research has suggested that nasopharyngeal samples are best suited for detecting respiratory viruses.
Some scientists also have practical interests. The mouth is “a slightly more uncontrolled environment than the nasal passages,” said Joseph DeRisi, a biochemist at the University of California, San Francisco, president of the Chan Zuckerberg Biohub and author of the cheek swab. . “Did you drink Coke right before taking the test? The pH will be different. And those things matter.”
Saliva can be “viscous and difficult to work with,” especially when patients are sick and dehydrated, Dr. Marie-Louise Landry, director of the Clinical Virology Laboratory at Yale New Haven Hospital, said in an email.
After all, different circumstances may require different approaches. Dr. Hansen suggested that for people who have had symptoms for several days, a nasal swab might be a good choice, while saliva might be best for large-scale surveillance of asymptomatic people. “We need to do the right test in the right places,” he said.