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Aug 6, 2020
DealBook’: Fast, Less-Accurate Coronavirus Tests May Be Good Enough
Experts
are revising their views on the best methods to detect infections,
setting aside long-held standards so that the spread of the virus can be
more quickly tracked and contained.
Credit...Avishek Das/SOPA Images/ZUMA Wire, via Alamy
For
months, the call for coronavirus testing has been led by one resounding
refrain: To keep outbreaks under control, doctors and researchers need
to deploy the most accurate tests available — ones reliable enough to
root out as many infections as possible, even in the absence of
symptoms.
That’s long been the dogma of infectious disease
diagnostics, experts say, since it helps ensure that cases won’t be
missed. During this pandemic, that has meant relying heavily on PCR
testing, an extremely accurate but time- and labor-intensive method that
requires samples to be processed at laboratories.
But as the virus continues its rampage across the country and tests remain in short supply
in many regions, researchers and public health experts have grown
increasingly vocal about revising this long-held credo. The best chance
to rein in the sprawling outbreaks in the United States now, experts
say, requires widespread adoption of less accurate tests, as long as
they’re administered quickly and often enough.
“Even
if you miss somebody on Day 1,” said Omai Garner, director of clinical
microbiology in the U.C.L.A. Health System. “If you test them
repeatedly, the argument is, you’ll catch them the next time around.”
This
quantity-over-quality strategy has its downsides, and is contingent on
an enormous supply of testing kits. But many experts believe more rapid,
frequent testing would identify those who need immediate medical care —
and perhaps even pinpoint those at greatest risk of spreading the
disease.
Such a considerable shift would likely be a welcome
change for a country where the status quo of testing was just described
as “unacceptable, period” by Dr. Anthony Fauci, the director of the
National Institute of Allergy and Infectious Diseases, in an interview
Wednesday on CNN.
“If you had asked me this a couple months ago, I
would have said we just need to be doing the PCR tests,” said Susan
Butler-Wu, a clinical microbiologist at the University of Southern
California. “But we are so far gone in this country. It is a
catastrophe. It’s kitchen sink time, even if the tests are imperfect.”
Of
the dozens of coronavirus tests that have been granted emergency use
authorization by the Food and Drug Administration, most rely on complex
laboratory procedures, like PCR, to detect the coronavirus’s genetic
material.
Only a handful are quick and simple enough to be run in
what is called a point-of-care setting, like a doctor’s office or urgent
care clinic, without the need for lab equipment. And these tests are
still relatively scarce nationwide. Government officials have pledged to
astronomically scale up the number of point-of-care tests by fall, increasing by millions the weekly tally of tests conducted.
But
many of the rapid tests at the center of this buzz still rely on
specialized machines that are neither cheap nor easy to produce in bulk.
And while some rapid tests, like the Abbott ID Now, were quickly adopted into the White House, most are unlikely to get much play in the larger community.
“We
can’t have these in every household,” said Michael Mina, an
epidemiologist at Harvard University’s School of Public Health and a vocal proponent of speedy testing.
Image
Credit...Carlos Osorio/Associated Press
A
better option, Dr. Mina said, might be antigen testing, which
identifies pieces of protein. Two such tests, made by BD and Quidel,
have received emergency authorization from the F.D.A. Both require
instruments to run, but even simpler versions of this technology could
provide a fast answer in the same way as pregnancy tests, allowing users
to swab their mouths or noses or spit into a tube, then read the
results as colored bars on a strip of paper within minutes.
These
tests could be done at a doctor’s office, or even at home — no fancy
machines or specially trained personnel required — and cost just a few
dollars a pop, perhaps even less. And there would be no delays of a week
or longer. Companies like the Massachusetts-based E25Bio are currently
cooking up tests that might fit this need.
Such convenient setups could resolve some of the supply shortages that have plagued testing laboratories across the nation for months
and caused a national embarrassment over inadequate, inaccessible
testing. In many cities, people are still experiencing turnaround times
of over a week, sometimes three or more — as people did at the beginning
of the U.S. epidemics — for results from PCR-based tests, effectively
rendering them useless for themselves and the people around them.
Hamstrung by a long delay, even an accurate test can morph into a useless one.
Natalie
Magnus, who got tested in Winnebago County, Ill., on July 14, still
didn’t have results 22 days later. Her brother and sister-in-law, who
were each tested twice at separate facilities in Colorado on July 7 and
July 8, have so far received only one set of results after a 17-day
wait. One of them was positive for the coronavirus.
Ms.
Magnus, who has already completed a two-week quarantine at home, no
longer cares if she gets her results. “By now, that doesn’t tell me
anything,” she said.
Antigen tests, on the other hand, can be
low-tech and easy to manufacture en masse. Distributed weekly or even
daily, they could painlessly screen people headed back into offices,
schools and universities, delivering peace of mind to parents, teachers
and employers. Everyone — not just those feeling ill — would have an
easier way to assess their health status on a regular basis.
“The
goal here is to detect as many infections as possible,” said Daniel
Larremore, an applied mathematician who models infectious diseases at
the University of Colorado, Boulder. “That means taking as many shots on
goal as we can.”
Broad distribution of antigen tests might also
ease the demand for PCR, which still has an important role in hospitals
and vulnerable communities like nursing homes. As things stand, many
doctors still can’t get their patients’ results within 24 hours.
In
those settings, accuracy is crucial, said Melissa Miller, director of
the Clinical Molecular Microbiology Laboratory for U.N.C. Hospitals.
“You don’t want to miss that diagnosis.”
There are drawbacks.
Antigen tests will miss some people who would test positive by PCR,
which amplifies coronavirus RNA and picks up even tiny amounts of it.
With antigen tests, proteins can’t be copied in the same way, making it
easier to mistake some people who are carrying minute levels of the
coronavirus in their bodies as pathogen-free. Some antigen tests used in
the past miss up to half the infections they look for.
Early
on, many experts balked because of these shortcomings. “As
laboratorians, we wanted the most sensitive test, the most specific
test, the most accurate test,” Dr. Miller said. “End of story.”
But Dr. Mina argues that false negatives might not be as bad as they seem.
Virus
levels vary from person to person, and can wax and wane in an
individual over the course of an infection, typically peaking around the
time symptoms first appear. People carrying — and thus probably
shedding — gobs of germs will most likely turn up positive using every
test on the market, Dr. Mina said. Those harboring less virus in their
bodies might get more mixed results. Many of these individuals, however,
probably aren’t the cases of most concern.
It’s another way to look at testing accuracy, Dr. Mina said: “Detecting the most infectious people.”
Image
Credit...Joe Raedle/Getty Images
A
testing rethink this substantial will inevitably come with snags. The
success of the speedy testing strategy hinges heavily on availability —
something the United States has utterly failed at since the virus first
made landfall within its borders. Ramping up antigen testing may only
add strain to an already sputtering supply chain, potentially hampering
plans for widespread use.
“If you test people all the time, you
can account for lack of sensitivity,” Dr. Butler-Wu said. “But are you
really going to test people all the time? If the answer is no, then that
lack of sensitivity becomes more of a big deal.”
And many experts
are still hesitant to trust negative antigen results, which may need to
be backed up with a more sensitive test. That might not be very
burdensome in the midst of an outbreak, when positivity rates are likely
to be high, Dr. Babady said. In spots where infection rates are
especially low, however, “that is not going to be the best approach to
testing,” she said.
Cheap tests also aren’t the same thing as free
tests. Even $1 tests can start to rack up quite a bill, especially for
large families hoping to do daily checkups or nursing home aides required to get tested repeatedly.
Left unregulated, the testing market could end up exacerbating the
socioeconomic split that’s already disproportionately burdened some
sectors of the population with the worst effects of Covid-19.
Concerns
over accuracy bogged down the approval process for simple, speedy
tests. F.D.A. guidelines stipulate that any new coronavirus test vying
for emergency clearance from the agency must perform nearly as well as the gold standard of PCR.
The
F.D.A.’s rules frustrate Dr. Mina, who noted that several companies on
the verge of debuting antigen tests have found the regulatory hurdles
daunting. “Many of them are not even bothering,” he said. “‘Our product
might not be good enough. So what’s the point?’”
That’s
left the onus on the few companies who already have the F.D.A.’s green
light. In hopes of encouraging a speedier, ramped up production, the
governors of seven states announced this week a joint bid to purchase a total of 3.5 million antigen tests from BD and Quidel.
There
probably isn’t one way to grapple with all these issues — and certainly
not an obvious one, Dr. Butler-Wu said. What’s clear to her and others,
though, is that the current situation is untenable.
“Our backs are against the wall, and it’s Hail Mary time,” Dr. Butler-Wu said. “We have to try something different.”
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