New saliva-based test on campus brings more frequent, less sensitive results

Numerous saliva-based tests have been approved by the Federal Drug Administration and used as a widespread COVID-19 testing method in many places — including at UNC.

UNC now offers free saliva-based testing Monday through Friday at the Student Union. Previously, the University only offered nasal-swab testing. While the test raises questions about sensitivity — compared to the traditional nasal-swab — the test allows students to get screened for COVID-19 more often. 

This widely available saliva-based testing had its accuracy questioned by numerous sources at its onset, said Audrey Pettifor, UNC epidemiologist and a member of the Campus and Community Advisory Committee. 

“The question was just, ‘Is there enough virus circulating in the mouth as there would be in the nose?'” Pettifor said. “In the last couple of weeks, a good bit more data has come out showing spit tests can be as good as the nasal swabs, if not better in some circumstances.”

Pettifor said the reliability of these tests largely depends on how good of a sample is being collected, meaning how much of the virus ends up in it. The most important component to any test is waiting the right amount of time before testing, she said. 

Dr. Melissa Miller, director of UNC’s clinical microbiology laboratory, said in an email that researchers really do not know how accurate most tests are on asymptomatic people. 

“In our experience, there was less virus present in saliva than in a nasal swab,” Miller said. “This was most pronounced in asymptomatic people who may have lower (concentration) of virus.”

Another concern with saliva-based testing is whether or not the samples will be saved after collection. But specimens collected at UNC are not stored after results are reported.

“The saliva specimens are sent to a commercial lab for testing,” said Ken Pittman, Campus Health executive director, in an email via UNC Media Relations. “After the test is run and the results are reported, then the specimens are discarded by the lab.”

Pettifor and Miller both said the key to successful testing using a saliva-based test is the frequency of testing. 

“If you are going to use a less sensitive collection method and/or a less sensitive test method, you really need to be tested more frequently, so you are detected as soon as possible once you have a higher viral burden,” Miller said. 

Increased COVID-19 screening resulted in fewer positive cases on campuses, even if the testing method was less sensitive, according to a study published in the JAMA Network Open medical journal. Using saliva-based tests as a surveillance measure has been practiced across many college campuses this semester with success. 

At the University of Illinois Urbana-Champaign, for example, undergraduate students are required to test for COVID-19 at least two times per week in order to enter any buildings on campus. As of Oct. 12, the school’s seven-day case positivity rate was at .24 percent, and the school had administered over 500,000 total tests. 

First-year Colby Taylor took both a traditional swab test and the saliva-based test and said he preferred the saliva-based test. Taylor said he believes other students will think the same.

“I have actually already taken the new saliva test because I was very curious to see if I could possibly have it and just be asymptomatic,” Taylor said. “The saliva tests are much less invasive than the swab tests.”

Taylor said he is hopeful that this testing method will allow the University to reopen next semester. 

“I believe the tests will help us to be able to come back to campus in the spring because it will help identify asymptomatic carriers of the virus faster,” Taylor said. “It will give the University the ability to more effectively control outbreaks.”

The gold standard for testing is still the traditional swab test, Pettifor said.

“It's considered the most sensitive test, meaning the most likely to detect a positive,” Pettifor said. “So if you go for a confirmatory test, like if you went to the hospital for a diagnostic test, they would do the nasopharyngeal swab that goes all the way up.”

The saliva-based test will be one of many factors that plays into the campus reopening, as its wide availability could make more frequent testing possible, Pettifor said. 

“The technology has advanced,” Pettifor said. “I think it makes sense to provide more saliva tests over nasal swabs, given the numbers of people that have been coming to the Student Union.”

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