Rapid Testing Is Less Accurate Than the US Government Wants to Admit
Rapid antigen testing is a mess. The federal government pushed it out without a plan, and then spent weeks denying problems with false positives.
 
The promise of antigen tests emerged like a miracle this summer. With repeated use, the theory went, these rapid and cheap coronavirus tests would identify highly infectious people while giving healthy Americans a green light to return to offices, schools and restaurants. The idea of on-the-spot tests with near-instant results was an appealing alternative to the slow, lab-based testing that couldn’t meet public demand.
 
By September, the U.S. Department of Health and Human Services had purchased more than 150 million tests for nursing homes and schools, spending more than $760 million. But it soon became clear that antigen testing — named for the viral proteins, or antigens, that the test detects — posed a new set of problems. Unlike lab-based, molecular PCR tests, which detect snippets of the virus’s genetic material, antigen tests are less sensitive because they can only detect samples with a higher viral load. The tests were prone to more false negatives and false positives. As problems emerged, officials were slow to acknowledge the evidence.
 
With the benefit of hindsight, experts said the Trump administration should have released antigen tests primarily to communities with outbreaks instead of expecting them to work just as well in large groups of asymptomatic people. Understanding they can produce false results, the government could have ensured that clinics had enough for repeat testing to reduce false negatives and access to more precise PCR tests to weed out false positives. Government agencies, which were aware of the tests’ limitations, could have built up trust by being more transparent about them and how to interpret results, scientists said.
 
When health care workers in Nevada and Vermont reported false positives, HHS defended the tests and threatened Nevada with unspecified sanctions until state officials agreed to continue using them in nursing homes. It took several more weeks for the U.S. Food and Drug Administration to issue an alert on Nov. 3 that confirmed what Nevada had experienced: Antigen tests were prone to giving false positives, the FDA warned.
 
“Part of the problem is this administration has continuously played catch-up,” said Dr. Abraar Karan, a physician at Harvard Medical School. It was criticized for not ensuring enough PCR tests at the beginning, and when antigen tests became available, it shoved them at the states without a coordinated plan, he said.
 
If you tested the same group of people once a week without fail, with adequate double-checking, then a positive test could be the canary in the coal mine, said Dr. Mark Levine, commissioner of Vermont’s Health Department. “Unfortunately the government didn’t really advertise it that way or prescribe it” with much clarity, so some people lost faith.
 
HHS and the FDA did not respond to requests for comment.
 
The scientific community remains divided on the potential of antigen tests.
 
Epidemic control is the main argument for antigen testing. A string of studies show that antigen tests reliably detect high viral loads. Because people are most infectious when they have high viral loads, the tests will flag those most likely to infect others. Modeling also shows how frequent, repeated antigen testing may be better at preventing outbreaks than highly sensitive PCR tests, if those tests are used infrequently and require long wait times for results. So far, there are no large scale, peer-reviewed studies showing how the antigen approach has curbed outbreaks on the ground.
 
People need to realize that without rapid testing, we’re living in a world where many people are unknowingly becoming superspreaders… Continue Reading…
 
Courtesy: ProPublica.org
 
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