U.S. government officials say a million promised tests for diagnosing coronavirus infections will soon be in the mail. But that still leaves many state and local laboratories without the ability to test for the virus, crucial for curbing its spread around the country.
Some states have developed their own
tests. Clinical testing companies are now joining the ranks. LabCorp
announced March 5 that physicians or other authorized health care
providers could already order its test. Quest
Diagnostics announced the same day that the company will also offer
commercial tests as soon as March 9, pending U.S. Food and Drug Administration
reviews. Participation of those two commercial laboratories could greatly
expand testing capacity in the United States.
But for now, “we still find ourselves as
a country with pretty limited capacity to test,” says Michael Mina, an
epidemiologist at the Harvard T.H. Chan School of Public Health in Boston.
Here’s what you need to know about
coronavirus testing in the country.
What’s the status of testing?
As of March 11, 81 state and local public health laboratories in 50 states and Washington, D.C., have successfully verified COVID-19 diagnostic tests and are offering testing, according to the U.S. Centers for Disease Control and Prevention. But even states that have tests may have only a single kit, containing enough material to test just 700 people, Mina says.
As of March 13, roughly 14,200 tests have been conducted nationally, according to an analysis from the Atlantic.
That’s up from the 1,583 people that had been tested at CDC, as of March 5. Contrast that with the United Kingdom, where 20,388 people had been tested as of March 6. At that point, only 163 cases of COVID-19 had been detected there.
As of March 13, U.S. health officials have reported over 1,885 coronavirus cases across 47 states and Washington D.C., including 41 deaths. More cases can be expected as testing ramps up, experts say.
As more cases are found, health
officials will need to test contacts of people who carry the virus, and other
ill people in affected communities may demand tests, all escalating the need
for more tests.
Vice President Mike Pence told reporters March 5, “We don’t have enough tests today to meet what we anticipate will be the demand going forward,” according to CNN. But having companies’ tests in the mix could help testing ramp up.
To get a more complete picture of how
widespread the virus is in the United States, “we’re going to need
millions and millions and millions of tests,” said Anthony Fauci, director
of the National Institute of Allergy and Infectious Diseases in Bethesda, Md.,
during a CNN town hall on March 5.
How does a test work?
Health professionals will swab a
person’s nose or throat, collect phlegm coughed up from the lungs, or squirt
liquid into the nose, throat or lungs and collect the liquid again for testing.
Neither Quest nor LabCorp will collect such specimens, but doctors or other
health providers may send samples to the labs for testing.
Then, those samples are analyzed in a laboratory, where technicians must extract and purify the virus’s genetic material from the mucus, cell debris and other stuff in the samples. “That sample preparation process is usually the biggest bottleneck [in testing],” says Brent C. Satterfield, founder and chief scientific officer of Co-Diagnostics, a company based in Salt Lake City and Gujarat, India, that has developed its own coronavirus test. That test can be used clinically in Europe, but has not yet been approved for use in the United States, although other labs can use components of the company’s test to build their own diagnostic tests.
All of the coronavirus tests being used
by public health agencies and private labs around the world start with a
technique called polymerase chain reaction, or PCR, which can detect tiny
amounts of a virus’s genetic material. SARS-CoV-2, the virus that causes
COVID-19, has RNA as its genetic material. That RNA must first be copied into
DNA. “That’s a lengthy part of the process, too,” says Satterfield, adding 15
to 30 minutes to the test.
After that, the PCR can begin. The
process makes millions to billions of copies of selected segments of DNA. In
the case of the coronavirus, the CDC’s original test scanned for three of the
virus’s genes, but now tests for two. The World Health Organization’s test,
developed by infectious disease researcher Christian Drosten at the Charité – Universitätsmedizin
Berlin and colleagues, tests for three genes but is a bit different than the
CDC tests. The PCR step typically takes 45 minutes to an hour, Satterfield
Some assays give instant yes or no
readings, but others may also take time to analyze. All together, it may take
about three hours to complete a test, Satterfield estimates.
Can my doctor do the test?
PCR tests are not simple enough to do in
a doctor’s office.
In the United States, a doctor is now
allowed to decide if a test is warranted and collect the sample, but then must
ship the sample off for other trained professionals to prepare and test.
Testing was initially limited to only
those people with symptoms and a travel history to an affected area or contact
with a known case. On March 4, the CDC
relaxed some restrictions on who can get tested. “People still have
to be sufficiently sick and have failed a flu test” in order to qualify for
coronavirus testing, Mina says.
In some states, the positive test results are
called presumptive positives until the CDC can confirm them. In those cases,
the final official result may take days. LabCorp estimates that it will take
three to four days to return results to physicians.
Why can’t the virus be tested for like influenza?
Many doctors’ offices can do a rapid influenza
test. But those flu tests don’t use PCR, Satterfield says. Instead, they detect
proteins on the surface of the influenza virus. While the test is quick and
cheap, it’s also not nearly as sensitive as PCR in picking up infections,
especially early on before the virus has a chance to replicate, he says. By the
CDC’s estimates, rapid influenza tests may miss 50 percent to 70 percent of
cases that PCR can detect. The low sensitivity can lead to many false negative
Flu tests also aren’t as specific for a
particular virus strain as PCR is. About 5 percent to 10 percent of the time,
flu tests may mistake a different virus for the flu, creating a false positive
result. “Specificity is a big deal when you’re testing large numbers of people
who aren’t expected to be positive,” Satterfield says. “If you’re going to test
in one of the states that doesn’t have a coronavirus outbreak right now, with a
specificity of 90 percent, 10 out of every 100 people are going to show up
positive even though the coronavirus isn’t there yet.”
“Accurate diagnosis is a very high
imperative for this [coronavirus],” Satterfield says.
An additional benefit of a PCR test is
that it may be able to detect viruses earlier in an infection than a flu-style test
can, he says, perhaps not in the first day, but a couple of days into an
infection when the virus is replicating strongly, but the body’s immune system
hasn’t yet begun to fight and produce symptoms. “In every infectious disease I
know of, that is the most contagious period for a person; the point in time
when the virus has multiplied to its maximum capacity and the body has not yet
started to rein in on it,” Satterfield says. Being able to identify people in
that period and isolate them from others could help curb the spread of the
Why was broader testing delayed in the first place?
Delays started with a manufacturing flaw
in the CDC’s original PCR test, which caused components that detect one of the three
targeted viral genes to not work properly, the health agency says.
Those woes sound like user error to Co-Diagnostics’
Satterfield. “A lot of what they are seeing is probably due to inconsistent use
in the field,” he says. “Tests that work phenomenally well in the lab, when
they are sent to the field, sometimes just don’t work the same,” he says.
Co-Diagnostics’ test also uses PCR but
tests for only one gene versus three. “Sometimes the more complexity you have
in a test, the more things you have that can go wrong,” Satterfield says.
Some delays in getting testing off the
ground came from emergency measures enacted by the FDA, Satterfield says. Normally,
big medical testing labs, such as state health labs and companies like LabCorp
and Quest Diagnostics, are allowed to develop and validate their own tests. But
when the coronavirus was declared
a public health emergency on January 31, labs needed “emergency
use authorization” before using their tests to diagnose cases. Even
the CDC had to get permission to use its test. But on February 29, FDA
announced that labs could devise their own tests and use them clinically while
waiting for the agency to review their applications. “FDA does not intend to
object to the use of these tests for clinical testing while the laboratories
are pursuing an EUA,” the agency said
in a statement.
“It looks like there were some pretty
large blunders that led to some serious delays,” says Mina, the epidemiologist
at Harvard. “Instead of reducing the amount of testing at the start of an
epidemic … we should have been expanding it as quickly as possible and calling
for all hands on deck,” he says.
Those delays and the initial limitations
on who could be tested may have allowed some cases to slip through the cracks
and start community outbreaks in Washington and California.
Where can I get tested?
It will vary from place to place. If you have symptoms of COVID-19 — fever, dry cough and often fatigue — contact your doctor or local or state health department for more information. Do not go to the emergency room for testing, officials say.
— to www.sciencenews.org