Error Rates on Rapid Covid-19 Tests Put Nursing Homes on Edge
The new rapid Covid-19 antigen tests being sent to thousands of U.S. nursing homes in high-infection areas have a troubling flaw: They provide false negative results for about 15% of infected people.
As nursing home infections climb once again due to the resurgence of the coronavirus, a false negative test could prove dangerous and even fatal for facilities that don’t confirm the results and mistakenly provide access to an infected person, said Christopher Laxton, executive director of AMDA—The Society for Post-Acute and Long-Term Care Medicine.
“If you’re putting people into an environment where they may in fact have the virus, it just hasn’t been caught, you’re putting a lot of people at risk. And that certainly is true of staff, but it’s especially true for residents,” said Laxton, whose organization represents more than 50,000 medical directors, doctors and other providers who work in nursing homes and other long-term care settings.
The cheaper, faster tests—which diagnose Covid-19 infections in 15 minutes—are central to the Trump administration’s push to keep nursing homes safe. They’ll allow more facilities to screen and test residents and visitors, and provide weekly tests for employees—which the Centers for Medicare & Medicaid Services will soon require in upcoming guidance.
The stakes couldn’t be higher. As of July 24, nursing homes and other long-term care facilities in 42 states reported 59,506 Covid-19 deaths, according to the Kaiser Family Foundation. That’s 44% of all Covid-19 deaths in those states.
The Department of Health and Human Services said in an email to Bloomberg Law that negative antigen test results “from patients with symptom onset beyond five days, should be treated as presumptive” and shouldn’t be “used as the sole basis for treatment or patient management decisions, including infection control decisions.”
The HHS, the Food and Drug Administration, and the test manufacturers recommend confirming negative results with a more accurate polymerase chain reaction, or PCR, test if necessary.
The Trump administration already shipped 654 antigen testing devices to 635 nursing homes. It plans to send nearly 1,800 of the machines, which are made by Quidel Corp. and Becton, Dickinson & Co., within the next three weeks, said Adm. Brett Giroir, who heads the Trump administration’s Covid-19 testing efforts.
“By putting point-of-care (testing) in nursing homes we not only improve turnaround and protect our vulnerable there, but we offload a lot of the demand on the major laboratories” to process test results, Giroir said.
The new tests quickly identify certain proteins that are part of the coronavirus in samples collected by nasal swabs. The devices, the Sofia and Sofia 2 models made by Quidel and the Veritor Plus System by BD, can process between 20 or more tests per hour in steady succession using a technique known as “batch testing.”
Cheaper, Faster Tests
The Trump administration plans to provide each of the nation’s 15,400 nursing homes with one of the devices as they become available in the coming months, CMS administrator Seema Verma said.
BD, of Franklin Lakes, N.J., expects to produce about 8,000 testing devices per month by the end of August, said Troy Hopps, the company’s point-of-care business group leader. The company also plans to hike production of its antigen test kits to 2 million per week over the same period.
“That’s a fourfold increase,” Hopps said of the scaled-up production. “We knew this increased demand would be there, so BD has invested heavily into our manufacturing facilities to meet this demand,” he said.
BP will provide 750,000 test kits to the nursing homes that receive their first 2,000 testing devices from the HHS, Hopps said.
The Veritor analyzer costs about $300 and has a lifespan of two years or 3,500 tests, Hopps said. About 25,000 of the devices are already in use. The BD tests cost about $20.
Confirming Negative Results
After the Food and Drug Administration issued to Quidel its first-ever emergency use authorization for an antigen test in May, FDA Commissioner Stephen Hahn warned that “negative results do not rule out infection. With this in mind, negative results from an antigen test may need to be confirmed with a PCR test prior to making treatment decisions or to prevent the possible spread of the virus due to a false negative.”
Quidel didn’t respond to requests for comment.
PCR tests detect genetic material from Covid-19. They’re considered the gold standard for diagnosing Covid-19. But it can take two to seven days or more to process and get test results from outside labs. The average turnaround time is 4.27 days, up nearly a day since June, Giroir said.
The new rapid tests detect antigens, the proteins on the outside of the coronavirus that trigger the body’s immune response. Although faster and cheaper, antigen tests aren’t as sensitive as PCR tests. So the extra steps needed to confirm a negative result means the antigen tests alone can’t ensure the accurate identification of potentially infectious individuals, including nursing home staff, residents, and visitors.
Laxton said the error rate wasn’t a “fatal” problem and that the tests are a valuable tool.
‘Very, Very Helpful’
“It’s very, very, very helpful to have some sort of frequent and available test. That said, the false negative rate is concerning, and it needs to be mitigated by either frequent retesting, or additional screenings, or confirmation with the PCR,” Laxton said. “Whatever tools, a facility has in its tool chest, that’s what we’ve been advising our folks to do.”
BD’s antigen test, which also received emergency use authorization from the FDA, will detect 80 to 90% of positive patients and 100% of those who are negative, Hopps said.
But it’s not a “final diagnostic” test, he said. It’s an “aid to be able to help clinicians, health-care professionals, to really quickly assess and rapidly determine if someone is infected or not.”
“If the test comes back negative, even though we have very high confidence based on our performance, it is still the recommendation of the FDA that those patients get a PCR test,” Hopps said. Especially “if the health-care professional has a suspicion that the patient is showing symptoms,” he added.
Laxton said he raised concerns about the error rates during a stakeholder conference call with HHS officials. He said the officials acknowledged the rate of false negatives, but said they believed “it’s an acceptable level.”
The American Health Care Association, the leading nursing home industry trade group, said in an email that packaging for both tests indicates that negative tests should be considered “presumptive” and confirmed with a PCR test.
“We are currently advising providers to follow their state and local public health guidelines and requirements for use of these tests. In addition, proper administration of tests, including sample collection and device maintenance, is critical to improve the accuracy of the results,” the group said.