Genetic testing of saliva for COVID-19 is just as accurate as approaches using nasal swabs and may spot the virus sooner, a new study has found. File photo by Debbie Hill/UPI | License Photo
March 21 (UPI) -- Genetic testing of saliva identifies the virus that causes COVID-19 more rapidly than screening of nasal swabs, a study published Monday by the journal Microbiology Spectrum found.
From three days before symptoms developed until two days after, saliva testing was up to 12 times more likely to detect the virus compared to evaluations of nasal swabs, the data showed.
Saliva samples collected for genetic testing also had three-fold higher levels of virus cells than nasal specimens, the researchers said.
Testing of saliva also was more likely to spot the virus early on in the course of infection, when people are at their most contagious, according to the researchers.
During the early period following infection, saliva testing accurately detected the presence of the virus 91% of the time, compared to 45% for nasal swab testing, they said.
However, from three to eight days after symptom development, saliva testing accurately detected the presence of the virus 89% of the time while nasal swab testing did so 94% of the time, the data showed.
In addition, the asymptomatic participants whose saliva samples tested positive showed symptoms of the virus one to two days later, the researchers said.
"Saliva testing works," study co-author Dr. Donald K. Milton told UPI in an email.
"It can detect infection earlier when it is most contagious, and it is also cheaper, as well as less bothersome, to collect than nasal swabs," said Milton, a professor of occupational and environmental health at the University of Maryland School of Public Health in College Park.
PCR testing of samples collected from the nose has been used to identify respiratory infections for decades, according to the American Society for Microbiology.
The tests are extremely accurate, but also expensive, costing consumers up to $500. Most insurers, at least until recently, have been covering 100% of these charges, the University of Rochester Medical Center noted.
In addition, many cities across the country have been providing the tests free to the public.
However, early in the pandemic, demand for testing led to a shortage of supplies, particularly for the nasal swabs used to collect samples.
Previous studies have found saliva testing to be just as accurate as approaches using nasal swabs.
For this study, Milton and his colleagues collected nose and saliva samples from 58 volunteers, 14 of whom tested positive for COVID-19.
In saliva testing, a person spits or drools into a test tube, puts a cap on the test tube and submits it for testing, according to Milton.
As with nasal swab testing, genetic testing of saliva uses PCR technology to detect the presence of virus, he said.
However, the approach evaluated in this study uses the SalivaDirect method developed at Yale University, which promises faster results at a lower cost than PCR testing of nasal swabs, Milton said.
It is able to lower costs because it does not require swabs to collect samples and entails "fewer lab steps and supplies," he said.
Saliva testing is less invasive and causes less discomfort than collection via nasal swabs and helps limits close contact between patients and healthcare workers, he added.
Saliva testing "can potentially identify infection earlier before it is transmitted, and it is easy to collect and cheaper." It has the potential to make "PCR testing more accessible, including in low- and middle-income countries," he said.