Researchers from the University of Arizona conducted a study on the rapid antigen test made by Quidel, as reported earlier this month by The New York Times. When testing asymptomatic patients or people who did not feel sick, the test only accurately detected 32 percent of the positive cases reported by a slower, lab-based PCR test.ae0fcc31ae342fd3a1346ebb1f342fcb In the study, researchers tested around 2,500 people from June to August. For the 1,551 people randomly selected with no symptoms, 19 tested positive with PCR tests. However, the rapid test only caught six of those cases. And for more on COVID spread, This Is When Someone Is Most Likely to Give You COVID, Study Shows. Unlike asymptomatic cases, this rapid COVID test could detect more than 80 percent of coronavirus infections reported by the PCR test. Of the 885 people that had either experienced COVID-like symptoms or been exposed to the virus, 305 tested positive with the PCR test. The rapid test caught 251 of those, missing 18 percent. “The data for the symptomatic group is decent,” Jennifer Dien Bard, PhD, the director of the clinical microbiology and virology laboratory at Children’s Hospital Los Angeles, who was not involved in the study, told The New York Times. “But to get less than 50 percent in the asymptomatic group? That’s worse than flipping a coin.” And for coronavirus symptoms to be on the lookout for, These 4 Easy-To-Miss Symptoms Could Mean You Have COVID, Experts Say. According to The New York Times, the U.S. Food and Drug Administration (FDA) only authorizes the use of Quidel tests for people with symptoms, yet the use of rapid tests for asymptomatic people has been “strongly encouraged by the federal government.” Even the Centers for Disease Control and Prevention (CDC) cautions the public against using a negative result from a rapid COVID test as their only source of judgment. The CDC says there is still only “limited data to guide the use of rapid antigen tests as screening tests on asymptomatic persons to detect or exclude COVID-19, or to determine whether a previously confirmed case is still infectious.” And for more on the limitations of this form of testing, discover What the White House Outbreak Has Taught Us About Rapid COVID Tests. David Harris, PhD, a stem cell researcher and an author on the study, said that the antigen tests may have missed certain asymptomatic patients because they were carrying too little of the virus to spread to someone else. The CDC says rapid antigen tests “detect the presence of a specific viral antigen,” meaning if they can’t detect enough coronavirus material to give a positive result, there may not be enough of a viral load to infect others. According to Harris, researchers weren’t able to grow the live coronavirus from samples of volunteers who had C.T. values above 27. And of the 13 asymptomatic patients missed by the Quidel test, 12 had C.T. values in the 30s. “If I don’t have live virus, I am not infectious at all,” Harris explained to The New York Times. And for more up-to-date information, sign up for our daily newsletter. Omai Garner, PhD, the associate director of clinical microbiology in the UCLA Health System, who was not involved in the study, told The New York Times that there is no proof that failing to grow the coronavirus from a person’s sample means they are not contagious. And other experts noted that the University of Arizona did not track coronavirus transmission from the participants, so they can’t make conclusions about the virus’ spread. Either way, people should not rely on rapid antigen tests when it comes to negative results. Susan Butler-Wu, PhD, a clinical microbiologist at the University of Southern California, who was not involved in the study, told The New York Times that people, especially those with known exposure to the coronavirus, should still get more precise and reliable PCR tests. And if you’re worried about getting sick, This Is the Easiest Way to Tell If You’ve Been Exposed to COVID.
