“Many people are mistaken in thinking that testing protects against covid,” Joshua M. Sharfstein, a professor at the Johns Hopkins Bloomberg School of Public Health and former deputy commissioner of the Food and Drug Administration, said in an email. “What protects against covid is masking, hand-washing and distance. Testing just helps identify covid when it happens, creating a chance to limit spread.”
President Trump has taken different approaches to testing in recent months. Early on, he left test acquisition to governors and mayors, then he sought to get testing kits to people faster, then he said the reason the number of positive test results was going up was that the United States was doing too much testing.
“I put a mask on, you know, when I think I need it,” Trump said at his debate against former vice president and Democratic presidential hopeful Joe Biden, whom he mocked for so often wearing a mask. Trump, who some doctors believe was already infected, said, “Tonight, as an example, everybody’s had a test and you’ve had social distancing and all of the things that you have to.”
Sharfstein said the White House has acted as if testing in and of itself confers protection. “It’s not to say testing isn’t important, but it’s part of a responsible approach to the virus,” he said. “It’s not the whole thing.”
The White House has not disclosed which brand of test or how many tests Trump took this week. Trump physician Sean P. Conley, a Navy commander, said that he obtained “PCR confirmation of the President’s diagnosis.” PCR stands for polymerase chain reaction, a method of detecting viruses that is considered the gold standard for accuracy.
But even the most sensitive tests will fail to detect the early stages of the virus and some people who are infected can keep testing negative for a few days.
Republican National Committee Chairwoman Ronna McDaniel, for example, saw Trump a week ago at a Sept. 25 fundraiser, then tested positive for the virus Wednesday. It remains unclear when she was infected and when her infection became contagious.
“It’s helpful to keep in mind that tests discover the presence of coronavirus once there’s enough viral material in a person to be able to detect it,” John Koval, spokesman for Abbott Labs, said in an email. “No test detects the virus immediately after the person becomes infected. There is no such thing as a 100 percent perfect and instantaneous test — for any disease.”
Some academic institutions have said that Abbott’s ID Now test misses infections 20 to 30 percent of the time. Koval said that the Abbott test “performs in the mid-80s to mid-to-high 90s when used as intended.”
The first step of any coronavirus test in the White House involves taking a swab and getting a sample from deep inside the nasal passages, nose or throat. When using the Abbott ID Now test, the swab, which can be as long as 15 centimeters, is then wiped into a device about the size of a toaster.
The device “amplifies” any strands of the coronavirus so it can be easier to detect. This technique, developed in the 1980s, uses the ability of DNA polymerase chains to synthesize new strands and make billions of copies of the sequences that are unique to the virus.
Within five to 13 minutes, the device gives a positive or negative reading.
Rapid point-of-care tests such as Abbott’s can screen large groups. The next logical step would be to take a test that has even greater certainty. The more rigorous PCR test — also manufactured by big companies such as Abbott Labs — takes about 6½ hours to analyze in machines that can handle a couple thousand samples at a time. Bottlenecks with the commercial labs, resulting from travel times or waiting for turns for PCR machines, have slowed down the testing time for most people to anywhere from two to 12 days, though recently the times have come down.
Clearly, the president did not wait that long. It is almost certain his initial test result was followed by a further, more reliable test, indicating he did indeed have the coronavirus. “As you know, last night, even in the early hours of this morning, the minute we got a confirmatory test on the president, we felt like it was important to get the news out there at that time,” White House Chief of Staff Mark Meadows told reporters Friday.
Meanwhile, the White House continues its rapid test strategy. “A number of us in the core team of the White House continue to get tested on a daily basis like we are — like we have been,” Meadows said Friday.