South Florida deploys rapid coronavirus antigen tests
At the peak of Florida’s July COVID-19 surge, state officials flooded Miami-Dade County’s state-run testing sites with rapid diagnostics designed to be used only on people with symptoms. The tests, which identify a protein on the virus called an antigen, are less sensitive than the tests more commonly used, called PCR tests, but antigen tests can produce results in minutes rather than days.
Was the trade off worth it?
Florida health officials are still figuring it out, and Miami-Dade has become a proving ground for the tests.
Jackson Health System, the county’s public-hospital network, started using antigen tests on patients less than a week ago. And Hard Rock Stadium in Miami Gardens and Marlins Park in Little Havana are the only state-run test sites that offer the antigen tests, a different brand than Jackson uses, with plans for adding more antigen testing to sites in Broward and
Palm Beach next week.
But the accuracy of antigen tests is not well understood, and there is not yet an agreed-upon protocol for notifying patients of their results. At Jackson Health, doctors are still confirming all negative antigen test results with PCR, or molecular tests.
“You can’t judge the performance of a test like that in less than a week,” said Dr. David Andrews, the head of Jackson’s laboratory, who said the hospital system’s initial validation of the test found that it captured about 70% of the positives picked up by the molecular tests. “We’re still growing into the test, and that’s going to be the challenge everywhere.”
Jackson’s validation study was based on about 50 emergency-room patients who were swabbed with antigen tests and later tested a second time with molecular tests.
But at the Hard Rock Stadium and Marlins Park testing sites, which are run by the state in partnership with the county, there is no second test to confirm negative results
The state of Florida and Miami-Dade County are working together to deploy more than 1,000 rapid coronavirus antigen tests a day, but public-health officials have raised concerns about how the results are reported.
of the antigen test.
Dr. Aileen Marty, a physician and epidemiology professor at Florida International University who advises Miami-Dade Mayor Carlos Gimenez on the outbreak, has stated that there needs to be one. She advised Gimenez that every negative antigen result should be confirmed with a molecular test.
“A negative antigen test means diddly squat,” Marty said. “A negative antigen test doesn’t mean you don’t have the virus to share — you could.”
State officials first turned to the tests as a way to identify COVID-positive people more quickly and, in turn, salvage floundering efforts to trace the contacts of confirmed cases as a way of reducing infections.
The Food and Drug Administration has authorized only two antigen tests for COVID-19. Both are being used in South Florida. And while the tests’ manufacturers report a high degree of accuracy, public health experts say that is influenced by a number of factors — most importantly, the infection rate in the community where antigen tests are used.
In Miami-Dade, where the rate of positive results out of all tests performed over the past two weeks has ranged from 11% to 18%, according to the state’s daily COVID reports, a false negative is more likely because of the high prevalence of the disease.
In New York, where the reported positivity rate is less than 1%, a negative result from an antigen test is more likely to be accurate because the disease is transmitting at a lower rate, said Tom Frieden, the former director of the Centers for Disease Control and Prevention.
“We have a misconception that a test has a fixed accuracy, and it doesn’t. It has an accuracy that’s based on the prevalence of the condition in the population,” Frieden said. “It’s a very important concept.”
The county has not yet committed to a plan for validating antigen test results. Deputy Mayor Maurice Kemp said that Gimenez is trying to bring as much antigen testing into the county as possible, and that the administration recognizes a trade-off between sensitivity and test results.
“We have to figure out what is the best test, and what is the best methodology,” Kemp said.
State officials sounded a similar note. Jared Moskowitz, director of the Division of Emergency Management, said there is no way for the state to mandate that those who test negative for antigen are then given a molecular test, though he said those tests are both available at the staterun sites.
Moskowitz said the department was likewise considering whether to implement a “control” process where two samples were collected and tested using both antigen and molecular tests. He added that the state was bringing antigen testing to two more sites in South Florida — one in Broward and one in Palm Beach — next week
“When we open up the two additional sites, we’re going to fine tune it,” Moskowitz said. “
... We may say to them, ‘Listen, if you get a negative test, here’s the [molecular] test, you should really get it done.’ ”
He said the two state testing sites that offer the antigen tests currently are seeing about a 5050 split on which test people are choosing to get, antigen or PCR, with about 600 of each per day.
Dr. Ashish Jha, director of the Harvard Global Health Institute, said antigen test results should be reported separately from PCR tests and added that the health department should make more information available on who is getting tested, how often the test is accurate, and whether it’s more accurate on people with symptoms.
“I am a fan of using antigen tests. I am a fan of the kitchen sink approach,” Jha said. “The problem is that if you don’t do it thoughtfully, you can’t learn how to do it better.”