For Coronavirus Testing, the Nose May Not Always Be Best

Saliva also has trade-offs. While the virus appears to accumulate in saliva early on, the nose may be a better place to detect it later during infection.

Researchers at the California Institute of Technology found that while the virus often rose first in saliva, it eventually rose to higher levels in the nose. Their results suggest that highly sensitive tests, such as PCR tests, may be able to pick up the infection in saliva days earlier than they do in nasal swabs, but that less sensitive tests, such as antigen tests, may not.

Some experts note that the data on saliva is still mixed.

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

But Dr. Hayden said she was interpreting the new studies with caution because “for years and years and years,” research has suggested that nasopharyngeal samples are best for detecting respiratory viruses.

Some scientists have practical concerns, too. The mouth is “a little more of an uncontrolled environment than the nasal passages,” said Joseph Derizzi, a biochemist at the University of California, San Francisco, president of the Chan Zuckerberg Biohub Foundation and author of the cheek swab paper. . “Did you drink Coke right before the test? The pH will be different. These things matter.”

Saliva can be “sticky and difficult to handle,” especially when patients are sick or 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 required in different circumstances. Dr. Hansen suggested that for people who have had symptoms for several days, nasal swabs may be a good option, while saliva may be best suited for a large-scale surveillance screening for asymptomatic people. “We need to do the right testing in the right places,” he said.

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