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Serial rapid antigen testing on par with PCR COVID-19 tests, RADx team reports

A longitudinal study co-authored by UMass Medical School researchers as part of the National Institutes of Health’s Rapid Acceleration of Diagnostics (RADx) initiative reported that PCR testing for SARS-CoV-2 and rapid antigen testing were equally effective in detecting infection when tests were given at least twice per week.

Study results represent good news for widespread prevention programs because antigen tests at the point of care or at home can deliver immediate results and are less costly than lab tests.

While individual PCR tests, considered the gold standard, are more sensitive than antigen tests particularly early in infection, the results showed that both testing approaches can give 98 percent sensitivity when taken regularly as part of a screening program, according to a news release from NIH. That’s good news for widespread prevention programs because antigen tests at the point of care or at home, available without a prescription, can deliver immediate results and are less costly than laboratory tests.

The study was published in the June 30 Journal of Infectious Diseases. UMass Medical School researchers who authored the paper along with researchers at the University of Illinois at Urbana-Champaign, Johns Hopkins School of Medicine and National Institute of Biomedical Imaging and Bioengineering were: Laura L. Gibson, MD, associate professor of medicine; Alyssa N. Owens, PhD, research coordinator; John P. Broach, MD, MPH, MBA, assistant professor of emergency medicine; Bruce A. Barton, PhD, professor of population & quantitative health sciences; Peter Lazar, application database developer; and David D. McManus, MD, the Richard M. Haidack Professor in Medicine and chair and professor of medicine.

“Rapid antigen testing at home, two to three times per week, is a powerful and convenient way for individuals to screen for COVID-19 infection,” said Bruce Tromberg, PhD, director of the NIBIB, part of NIH. “With schools and businesses reopening, an individual’s risk of infection can change from day to day. Serial antigen testing can help people manage this risk and quickly take action to prevent spread of the virus.”

Researchers collected two forms of nasal swabs and a saliva sample for participating employees and students in a COVID-19 screening program at the University of Illinois at Urbana-Champaign for 14 consecutive days. One of each participant’s nasal swabs was sent to a laboratory at Johns Hopkins University to observe the growth of live virus in culture, to obtain a rough measure of the period during which subjects could spread infection to others.

The researchers then compared three COVID-19 testing modalities: PCR testing of saliva, PCR testing of nasal samples and rapid antigen testing of nasal samples. They calculated the sensitivity of each test modality to detect SARS-CoV-2 and measured the presence of live virus over a two-week period following infection.

When researchers calculated test sensitivity based on a cadence of tests every three days, they reported better than 98 percent sensitivity to detect infection, whether using rapid antigen tests or PCR tests. When they assessed frequency of testing only once per week, nasal and saliva PCR testing sensitivity remained high, at around 98 percent, but antigen test sensitivity declined to 80 percent.

“The challenge with interpreting PCR or antigen test results is that a positive test may not indicate transmissible infection (low specificity) or may not detect live virus in the sample (low sensitivity), respectively,” said Dr. Gibson, who co-leads the RADx Tech Clinical Studies Core.

“The unique aspect of this study is that we paired PCR and antigen testing with viral culture as a marker of transmissibility. This study design revealed the best way to use each type of test and reduced the impact of challenges interpreting their results for patients suspected of having COVID-19.”

Nathaniel Hafer, PhD, assistant professor of molecular medicine and lead investigator of RADx Tech Study Logistics Core, said, “As an example of the impact of our work, the data we collected has helped to inform CDC guidance on the use of antigen tests in different populations.”

Dr. Hafer pointed to UMass Medical School’s critical role in the design, conduct and analysis of this work on testing sensitivity. He gave special recognition to the UMass Medical School study team—led by Dr. Broach and including Gul Nowshad, project director, and Bernadette Shaw, research navigator—that played a vital role remotely observing the participants who took part in this study in dorm rooms at the University of Illinois.

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