Saliva also has compromises. While the virus appears to accumulate in saliva early on, the nose may be a better place to spot it later in the infection.

Researchers at the California Institute of Technology found the virus frequently first speared in saliva, it eventually rose to higher levels in the nose. Their results suggest that highly sensitive tests like PCR tests can detect infection in saliva days earlier than in nasal swabs, but less sensitive tests like antigen tests may not.

Some experts found that the data on saliva are still mixed.

“There are these few studies that I found really interesting,” said Dr. Mary K. Hayden, an infectious disease physician and clinical microbiologist at Rush University Medical Center in Chicago.

Dr. However, Hayden said she is interpreting the new studies cautiously, as research “over years and years and years” suggests that nasopharyngeal specimens are best for detecting respiratory viruses.

Some scientists also have practical concerns. The mouth is “a little more uncontrolled compared to the nasal passages,” said Joseph DeRisi, 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 right before the test? The pH will be different. And these things are important. “

Saliva can be “viscous and difficult to handle,” especially when patients are sick and dehydrated, said Dr. Marie-Louise Landry, director of the clinical virology laboratory 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 may be best for large-scale surveillance screening of asymptomatic people, suggested Dr. Hansen before. “We have to put the right test in the right places,” he said.



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