Public Health Officials Pursue Covid-19 Tests That Trade Precision for Speed

Rapid tests for coronavirus might sacrifice some accuracy for quicker results but are needed to control the virus

By Brianna Abbott and Thomas M. Burton of The WSJ. Excerpts:

"Public health experts are increasingly calling for a shift in thinking about Covid-19 testing: It is better to get fast, frequent results that are reasonably accurate than more precise results after dayslong delays.

Diagnostic companies are racing to develop quicker, cheaper Covid-19 diagnostic tests, and tests that can be done at doctors’ offices, nursing homes and other places with the assistance of a medical provider are gradually becoming more widespread.

The U.S. Food and Drug Administration has authorized four such tests that are antigen-based, meaning they search for viral proteins. Test makers have vowed to produce tens of millions of these quick-turnaround tests in coming months, including Abbott Laboratories which recently unveiled a test that costs $5 and is the size of a credit card.

Several companies also are working on at-home rapid tests that people can perform themselves. No test is currently authorized for complete at-home use, in part due to regulatory requirements for ease-of-use and accuracy."

"Most Covid-19 diagnostic testing in the U.S. is processed in laboratories and uses a technique called rt-PCR that searches for the virus’s genetic material and amplifies it. The tests are incredibly sensitive but expensive to run, and the process often requires shipping samples from a test site to a lab."

"In July, demand for Covid-19 tests overwhelmed the major U.S. commercial laboratories, which delayed results for days or sometimes weeks, rendering much of the information practically useless."

"What is needed, some public-health specialists say, is a shift to cheaper, more routine testing among people who don’t show any symptoms to identify those who can potentially spread the virus. That would involve making a distinction between Covid-19 testing for patient diagnosis and testing for public-health screening.

For one-shot diagnostic testing, doctors need tests that are relatively quick but as accurate as possible. But for screening purposes in settings such as workplaces or prisons, a less-sensitive test, such as an antigen test, would be good enough to catch most cases and isolate those with an infection while relieving pressure on labs.

With frequent testing, cases missed the first time around might be caught a few days later. That is more effective for screening than a highly-accurate test done once a month or once a week, which would give the virus more time to spread, public health authorities say."

"Antigen tests are better at identifying cases when people have more virus in their system—meaning they will likely find people when they are most infectious"

"A high regulatory bar for authorization is one reason quick, at-home testing for consumers has yet to hit the market"

"At-home test manufacturers have to show the FDA that the public can grasp the instructions, take the test and interpret results correctly, without assistance. If the manufacturer wants authorization for a test that can screen asymptomatic people, it must meet an additional set of standards."

"The FDA also has said that rapid tests should have comparable accuracy to PCR diagnostic tests—a requirement that some public health specialists and companies say is overly stringent for surveillance testing."