Saliva also has compromises. While the virus may appear to accumulate in saliva early on, the nose may be a better place to detect it later in the course of the infection.
Researchers at the California Institute of Technology found that while the virus often stings saliva first, it eventually rose to higher levels in the nose. Their results suggest that highly sensitive tests, such as PCR tests, can pick up infections in saliva days earlier than in nasal swabs, but less sensitive tests, such as antigen tests, may not.
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The data on saliva is still mixed, some experts noted.
“There are a few studies that I’ve found really interesting,” said Dr. Mary K. Hayden, an infectious disease physician and clinical microbiologist at Rush University Medical Center in Chicago.
But dr. Hayden said she interpreted the new studies with caution because “years and years and years” of research has suggested nasopharyngeal specimens are best for detecting respiratory viruses.
Some scientists also have practical concerns. The mouth is “a bit more of an uncontrolled environment compared to the nasal passages,” said Joseph DeRisi, a biochemist at the University of California, San Francisco, who is a president of the Chan Zuckerberg Biohub and an author of the cheek swab. . “Did you drink a Coke right before taking the test? The pH will be different. And those things are important.”
Saliva can be “viscous and difficult to work with,” especially when patients are sick and dehydrated, said Dr. Marie-Louise Landry, director of the clinical virology lab at Yale New Haven Hospital, in an email.
Ultimately, different approaches may be required in different circumstances. For people who have had symptoms for several days, nasal swabs may be a good choice, while saliva is best suited for large-scale surveillance screening of asymptomatic people, suggested Dr. Hansen. “We need to get the right test in the right places,” he said.