Saliva also has compromises. While the virus appears to accumulate in saliva early, the nose may be a better place to detect it later in the infection.
Researchers at the California Institute of Technology found that while the virus often first penetrated saliva, it eventually rose to higher levels in the nose. Their results suggest that highly sensitive assays, such as PCR assays, may be able to detect salivary infections several days earlier than nasal swabs, but that less sensitive assays, such as antigen assays, may not.
Coronavirus pandemics: Key things you should know
Saliva data are still mixed, some experts noted.
“There are a 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.
But Dr. Hayden said she interprets the new studies cautiously because “years and years and years” of research have suggested that nasopharyngeal samples are best for detecting respiratory viruses.
Some scientists also have practical concerns. The mouth is “a little more uncontrolled environment compared to the nasal passages,” said Joseph DeRisi, a biochemist at the University of California, San Francisco, who is president of Chan Zuckerberg Biohub and author of a paper swab. . “Did you drink a cola just before the test? The pH will be different. And that’s what matters. “
Saliva can be “viscous and difficult to work with,” especially when patients are sick and dehydrated, said in an e-mail. Marie-Louise Landry, director of the clinical virology laboratory at Yale New Haven Hospital.
Finally, different approaches may be required in different circumstances. For people who have symptoms for several days, nasal swabs may be a good choice, while saliva might be best suited for large-scale screening in asymptomatic people, suggested Dr. Hansen. “We have to get the right test in the right places,” he said.