Saliva also has compromises. Although the virus seems to collect early in the saliva, the nose may be a better place to detect it later in the infection.
Researchers at the California Institute of Technology have found that while the virus often rises in saliva first, it eventually reaches higher levels in the nose. Their results suggest that highly sensitive tests, like PCR tests, can detect infections in saliva a few days earlier than in nasal swabs, but less sensitive tests, like antigen tests, might not.
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Data on saliva is still mixed, some experts noted.
“There are these few studies that I found really 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 “for years and years” research has suggested that nasopharyngeal samples are the best at detecting respiratory viruses.
Some scientists also have practical concerns. The mouth is “a bit more of an 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 paper. . “Did you drink a Coke just before taking the test? The pH will be different. And those things matter.
Saliva can be “slimy 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. .
Ultimately, different approaches may be needed in different circumstances. For people who have had symptoms for several days, nasal swabs might be a good choice, while saliva might be better suited for large-scale surveillance screening of asymptomatic people, Dr. Hansen suggested. “We have to put the right test in the right places,” he said.