In-Depth: Why saliva might be superior to nasal swabs in the search for omicron

Saliva COVID test
Posted at 6:59 PM, Jan 25, 2022
and last updated 2022-01-25 23:28:24-05

SAN DIEGO (KGTV) – As cases of omicron have surged, so has interest in the optimal way to test for the variant. Are nasal swabs still the best? Or should people opt for a saliva test instead?

Alcala Labs is one of the few places in San Diego where people can spit into a tube and get a COVID diagnosis in 24 to 48 hours.

“You want to have [the test] in an area where the virus is a lot more concentrated, and that would probably be in the saliva,” said lab manager Eric Brunson.

Emerging research suggests saliva-based PCR tests may indeed offer the earliest opportunity to detect omicron. However, early studies offer a more messy picture for at-home rapid antigen tests. These tests operate differently than PCR, and there are signs saliva might make them worse.

In late December, researchers in South Africa compared the sensitivity of saliva and mid-nasal swabs for a PCR test. They found saliva performed best when the patient had the omicron variant, whereas nasal swabs were superior with delta. “Saliva swabs are the preferred sample for Omicron detection,” they concluded.

A pre-print from scientists at the University of Maryland found that in the early days of an omicron infection, the viral load is three times higher in saliva than in the nose. Using saliva instead of a nasal sample improves the chances of finding infection 12-fold, they found.

“With omicron, more than delta, you’re able to detect it in the saliva sooner than you are from your nose swab,” said Dr. Blythe Adamson, an epidemiologist who oversaw another study comparing testing types.

“The first thing that will test positive is the saliva PCR. And then maybe the next day the nasal PCR. And then maybe the nasal rapid-antigen the next day, or another day after that,” she said.

Keep in mind: all of these studies evaluated highly sensitive PCR tests that were designed to handle saliva. Still, the results have motivated some people to experiment with saliva while taking an at-home rapid test.

In an online trend, some people have started swabbing both their throat and their nose against the manufacturer’s instructions. Currently, there is no rapid test validated for saliva in the U.S.

The trend has roots in a small study by a team at UC San Francisco. The researchers found that swabbing both the throat and nose with Abbott’s BinaxNOW rapid test improved the sensitivity from 85.7 percent to 89.8 percent. The study only examined that particular test.

The Food and Drug Administration says improperly swabbing the throat can cause injury. The agency encourages people to follow the manufacturer’s instructions.

“The environment in the mouth is very different than the environment in the nose,” said Sharp Healthcare laboratory medical director Dr. Omid Bakhtar.

Different at-home tests use different chemicals or reagents. Some might work with saliva, but enzymes in the mouth might interfere with others, Bakhtar said.

Scientists in Spain tried doing cheek swabs with three kinds of rapid tests designed for the nose: BIOSYNEX COVID-19 Ag BSS, FLOWFLEX, and Panbio. Panbio is a rapid test made by Abbott for sale outside the U.S. The company says it uses “similar biologics” to BinaxNOW.

Last week, the team released their results: the cheek swabs missed 68 percent of the infections that were otherwise detected with a nasal sample.

“If you go outside the realm of the instructions of what the test says, then yes, you can invalidate that test,” said Brunson, the lab manager of Alcala Labs.

For now, the only COVID tests authorized for saliva are ones processed at labs.