Because the new coronavirus is primarily an upper respiratory disease, inserting a thin swab deep into the nasal cavity has become the primary method of testing.
But the virus can also be detected in saliva, and early research by scientists at the University of Chicago found that saliva-based digital tests are just as accurate.
"The saliva test is comparable to a nasal swab, which is encouraging," said Evgeny Izumchenko, assistant professor of medicine in UChicago's hematology and oncology program. "The advantage (of a saliva-based test) is that it's less invasive and you can have people collect their own samples. Everyone knows how to spit."
Scientists believe that saliva testing can eliminate inconclusive test results in patients who are negative for the virus but still show symptoms. That's because saliva testing uses a system called droplet digital PCR to measure the amount of virus in a sample, while swab testing uses a technique called qPCR to detect only the presence of the virus.
Nishant Agrawal, a Chicago surgeon, researcher, said in a statement, "Saliva testing can provide clinicians with a quantitative amount of virus present, not just a simple yes or no." Agrawal has been involved in digital PCR and saliva research for more than a decade.
The researchers also believe that saliva testing can more accurately identify cases that are asymptomatic. "It's possible that people who have the virus but don't show symptoms may not show up in small amounts on traditional tests," Jeremy Segal, an associate professor and pathologist at UChicago, said in a statement. "If they are still able to transmit the virus, it will be very important to be able to detect these people."
Izuchenko said saliva testing may also be used to ensure that COVID-19 patients do not have traces of the virus before they are discharged from the hospital.
With a surge of coronavirus cases in Chicago in late March and early April, researchers set up a booth at UChicago Medicine's roadside COVID-19 testing site and asked people who had been examined by health care workers if they would like to participate in the study by spitting saliva into a test tube and then sampling it via a nasal swab.
Researchers performed droplet digital PCR tests on nasal swabs and saliva samples in the Savas Tay lab at the Pritzker School of Molecular Engineering and compared the results to those of hospital samples using qPCR testing.
The study is ongoing, but so far the saliva test samples collected are in perfect agreement with the hospital results.
