With fewer people getting tested for COVID, Florida turns to rapid tests for a boost

Ben Conarck
·6 min read

At the height of Florida’s summer COVID-19 surge, with cars snaked in single-file lanes waiting to get tested and results not coming until weeks later, public health efforts to trace and isolate the virus’ spread ground to a halt.

By the time Florida officials fixed the problem — ditching slow-moving labs, offering quicker tests and cutting wait times — the number of new people getting tested per day had dropped by more than half, from 25,000 to 30,000 since September, versus approximately 60,000 in late July, according to the COVID Tracking Project.

Jared Moskowitz, Florida’s testing czar, said he often fields questions about why testing in Florida has been largely trending down.

“People were looking for some sort of boogeyman in that answer,” he said. “And truthfully, the answer was, people were just not coming to get tested.”

But Moskowitz also conceded that even waiting hours for a “rapid” test result, or a day or two for a more-sensitive molecular test, goes against a natural human instinct of wanting an immediate answer.

The first test capable of providing a reliable and truly rapid test result is just starting to arrive in Florida. It detects the antigen protein on the surface of the virus at about 94% sensitivity — meaning it is accurate 94 out of 100 times — and delivers results in about five to 15 minutes.

That’s roughly five times faster and considerably sharper than the previous “rapid” antigen tests the state was using at its drive-thru sites. Those tests will now be discontinued.

High-sensitivity molecular polymerase chain reaction, or PCR, tests, will still be available upon request and will be recommended for people with symptoms who test negative on a rapid test, officials said. Those results can still take one to three days, on average.

New rapid tests rolling out in Florida

The state is already using the new rapid test, manufactured by Abbott Labs, called the “BinaxNOW,” at a couple of sites in North Florida, and plans to roll them out to every state-run drive-thru by Saturday.

The North Florida sites with rapid tests have seen spikes in the number of people showing up, and Moskowitz said they are sticking around the parking lot waiting for a five-minute result, as opposed to driving off to be contacted by phone or text later.

In Jacksonville, a rapid test site was averaging nearly 1,200 tests per day over the last week, up from 221 per day in the week before, when the site didn’t have rapid testing, officials said.

That’s a worthwhile sacrifice for about a 5% less accurate reading over the PCR test, which typically catches the virus 99 out of 100 times, or more, if performed properly, said Michael Mina, an infectious disease expert at Harvard’s T.H. Chan School of Public Health. The PCR test was the default until this weekend.

“If it can draw more people in, that’s really all I care about,” said Mina, who added that it was understandable that people would be more enticed by a faster test. “ ... Humans like immediate feedback; so in that sense, these tests can be quite powerful.”

Mina said the 95% sensitivity for the BinaxNOW test holds only when they are used by trained medical professionals — as they will be at Florida drive-thrus — and cases are detected within the first seven days of infection. He downplayed concerns over the lower accuracy of the test and how it might miss people who are not yet showing symptoms.

“The test doesn’t care if you’re asymptomatic or symptomatic; the test cares if you have a lot of virus in your nose,” Mina said. “And that’s what we care about — if we’re worried you’re going to transmit to other people.”

Debate over infectious window

The trade-off between sensitivity and turnaround time on test results has been debated by scientists since the pandemic began, but the conversation heated up in July, when Mina wrote an op-ed in the New York Times arguing for more emphasis on the frequency and cost of testing rather than the sensitivity of the assay.

By the end of the month, Moskowitz, the testing czar, had bought into the idea of faster antigen testing, and begun to shift the state toward them by including them at state-run testing sites. The latest iteration of the antigen test, the BinaxNOW test, was acquired from the U.S. Health and Human Services Department, which bought out the entire supply and shipped it to states for free.

But the tests are not without their critics.

Dr. Aileen Marty, who teaches epidemiology at Florida International University and advises local officials on public health measures, has raised concerns over the sensitivity and specificity — or the ability to rule out infections — of antigen tests, which are more prone to false negatives and false positives.

The key issue for Marty is timing, in that PCR tests can detect the virus at an earlier stage in the course of an infection than antigen tests could. Although someone might wait around for PCR results longer, there’s also a risk in someone testing negative with a rapid test after an exposure, then becoming infectious days, or even hours later, she said.

“Unless they use the test VERY judiciously, they are likely to have many false negatives that lead to more outbreaks,” Marty wrote in an email.

Addressing the concern that a PCR test is more likely to detect the virus than an antigen test in someone who hasn’t shown symptoms yet, Mina said that pre-infectious window of detection was likely as short as a day or two for either test.

“This is where we don’t have enough people taking a big step back and saying, ‘What matters here?’” Mina said. “What matters is the overall number of people we can find that are infectious. So if this means we can scale up the number of tests tenfold, but we are missing a few people who would otherwise be caught with a PCR test in a pre-infectious window, that’s really rare.”

Gigi Gronvall, an immunologist and senior scholar at the Johns Hopkins Center for Health Security, said false positives from antigen tests have tended to come from user or test error. The problem with antigen tests, she said, tends to be false negatives for people early on in their infection with a lower viral load.

“That is a problem, but when someone is positive, they probably have a lot of virus,” Gronvall said. “A lot of people are starting to think that it’s okay to prioritize, and to get those people out of circulation.”