Illinois' top doctor on Friday defended the use of rapid antigen tests to detect COVID-19 as reports of false negatives and false positives surfaced nationwide, leading to questions about accuracy.
In one instance that garnered nationwide attention, tech entrepreneur Elon Musk tweeted he took four COVID-19 rapid antigen tests on Thursday, and received two negative and two positive results.
Musk, who has been dismissive about the coronavirus and its severity, said he took two PCR tests, the other type of COVID-19 tests, and was awaiting results, CNBC reported.
At Illinois' daily coronavirus news briefing Friday, Dr. Ngozi Ezike, the director of the state's public health department, said both antigen and PCR tests have accuracy rates above 90%, but acknowledge PCR tests are the "gold standard."
PCR tests detect the virus’s genetic material and are much more sensitive compared to antigen tests, which detect specific proteins from the virus and are much quicker, according to the U.S. Centers for Disease Control.
"Take a pregnancy test. You can have a blood test. You can have the one you can get from the drug store...the dollar store," Ezike explained. "You will still use that and know its going to give you a reliable result. Are there a few cases in which it wont be perfect? Yes, that’s true, but that doesn’t mean you’re going to throw away a positive pregnancy test, and say there’s no way you can be pregnant."
With PCR tests, sometimes results are available on the same day, but that's not always the case. Results of rapid antigen tests are often available in 15 to 30 minutes, the CDC stated.
"We have a test that is good that will give us accurate results," Ezike said in reference to rapid antigen tests. "It helps us identify cases even sooner, which is so important when you’re trying to have the people who are infected isolate as soon as possible instead of spreading it around in the interim while waiting for the PCR result."
Illinois began distributing rapid antigen tests from the federal government last month, and Ezike expects as more of those tests are conducted "we will get more probable cases."
Beginning Friday, Nov. 6, Illinois health officials began including "confirmed cases and probable cases combined" under guidance from the CDC.
A large portion of the state's "probable" cases came from an increase in antigen testing across the state, in part sparking the change in reporting, Dr. Ezike said.
On Friday, Gov. J.B. Pritzker blasted those who he said are "kind of some sort of conspiracy" about rapid tests, emphasizing the state will use all types of tests that are available.
"That’s a huge benefit to be able to tests lots and lots of people in a very short period of time," he added. "So we’re going to take advantage of the fact the federal government sent us those tests."
Illinois on Friday reported more than 15,000 new confirmed and probable coronavirus cases, setting a record for the highest single-day report of new cases for the fourth consecutive day.