Public health strategies that aim to curb the spread of the novel coronavirus by frequent, rapid testing may have limited efficacy, as demonstrated in part by the spread of Covid-19 among President Trump and those connected to him, according to public health experts.
Tests being used to detect the coronavirus vary
USA Today reports that the most sensitive test for the novel coronavirus is currently the polymerase chain reaction (PCR) test, which, according to Richard Scanlan, chair of the College of American Pathologists Council on Accreditation, can detect the virus within four days of infection. However, these tests, which require a DNA sample taken via a nasal swab, are typically evaluated at labs and can take days to process. Some providers have access to portable machines with can process these tests in less than one hour, USA Today reports.
In comparison, antigen tests—which detect the coronavirus' proteins—are less costly and often quicker to produce results than PCR tests. However, according to Scanlan, these types of tests are not as sensitive as PCR tests, and they usually can't detect the coronavirus until at least seven days after infection. In fact, according to Alan Wells, medical director of clinical labs at the University of Pittsburgh Medical Center, antigen tests can miss up to 50% of positive cases that PCR tests can detect among certain patient populations.
Moreover, Lewis Nelson, professor and chair of emergency medicine at Rutgers New Jersey Medical School, cautioned that any test is administered in just one moment in time—meaning that someone who had a negative test could test positive for infection just moments later. "It's a total slice in time that in that moment you're negative," he said. "The moment your test comes back negative, you are no longer negative."
Many people connected with Trump test positive for Covid-19
Recently, KHN reports, many individuals who came in close contact with Trump—who tested positive for the novel coronavirus on Thursday, Oct. 1—have since tested positive themselves, a trend that public health experts say highlights the shortcomings of using only rapid testing as a coronavirus containment strategy.
Since Trump's positive test, at least seven people who attended Trump's formal nomination of Judge Amy Coney Barrett to the Supreme Court on Sept. 26, have tested positive for the novel coronavirus, KHN reports. Moreover, at least 11 people involved in the presidential debate on Sept. 29 have tested positive, even though everyone who attended underwent testing and abided by other measures, including social distancing, hand sanitizing, and temperature checks. On Tuesday, Stephen Miller, Trump's top speechwriter and a policy adviser, announced he'd tested positive for Covid-19 and is quarantining.
Experts say because of the way the virus incubates and spreads it's possible that other people may report infections. "You are probably not detectable for three, five, seven, even 10 days after you're exposed," Wells said.
For instance, one of the individuals who attended the Rose Garden event—Kayleigh McEnany, the White House press secretary—on Monday announced that she had tested positive for the novel coronavirus—after testing negative "every day since Thursday."
Experts voice caution
According to Kaiser Health News, the White House has largely relied on antigen testing to contain and curb the novel coronavirus' spread.
The test the White House is currently using—Abbott Laboratories' BinaxNOW—received an emergency use authorization from FDA in August. According to Abbott, the test—when used to assess people within seven days of experiencing symptoms—is 97% accurate in detecting positive cases and 98.5% accurate in detecting people who aren't infected. However, according to KHN, little independent research has been conducted on the test.
However, public health experts and Trump administration officials have said relying on frequent testing alone as a Covid-19 containment strategy is problematic. That's in part because—no matter how accurate or sensitive the test—someone may have such minute traces of the coronavirus that they don't test positive for several days after infection, even if they do have enough of the virus to be infectious themselves.
It's "what we call a window period: that's the period after you get infected and before you test positive," Scanlan said.
Isaac Bogoch, an infectious disease specialist at the Toronto General Hospital Research Institute, said there are several reasons a test may miss a case of the novel coronavirus, including, but not limited to, improperly collected samples and malfunctioning equipment. Bogoch recommended that anyone exposed to the virus follow CDC guidance. Currently, CDC advises people who've come in close contact with someone who is infected to self-quarantine for at least 14 days, regardless of whether they test positive or negative for the coronavirus
In August, Adm. Brett Giroir, the senior HHS official helming the administration's testing effort, said, "Testing does not substitute for avoiding crowded indoor spaces, washing hands, or wearing a mask when you can't physically distance; further, a negative test today does not mean that you won't be positive tomorrow."
Wells also cautioned that testing "isn't a 'get-out-of-jail-free' card" (Alltucker/Rodriguez, USA Today, 10/5; Goodman, WebMD, 10/5; Pradhan et al., Kaiser Health News, 10/2; Haberman/Steinhauer, New York Times, 10/6).