Caution Arises on Rapid Covid Tests in Asymptomatic People
(Bloomberg) -- One of the first states to receive rapid, low-cost coronavirus tests from the U.S. government is cautioning against their use in asymptomatic people, a group that were hoped to benefit most from the technology.
Antigen tests like one from Abbott Laboratories that look for telltale viral proteins may miss some infections that can be picked up by costlier gold-standard assays, and can incorrectly return positive results. The rapid tests aren’t recommended for people without symptoms who haven’t been exposed to a Covid-19 patient, and those who undergo one should be informed of the limitations, the Louisiana Department of Health said in guidance issued last week.
The recommendations highlight issues with tests like Abbott’s $5 BinaxNOW that the U.S. Department of Health and Human Services is spending $750 million on and were used in the White House. State health officials are increasingly concerned that people without symptoms should be screened with more costly but more reliable polymerase chain reaction assays because of worries about the rapid tests’ performance, according to Jeff Engel, a senior adviser at the Council of State and Territorial Epidemiologists.
HHS “made this purchase without any studies on the novel use in which they’re deploying these tests,” Engel said. “I think that’s careless.”
HHS is providing antigen tests for use in symptomatic and asymptomatic people, said Mia Heck, an agency spokeswoman, in an email. Widespread, affordable rapid antigen testing helps slow the virus’s spread, and tests like BinaxNOW, when used as intended, can detect those most likely to be infectious, Abbott said in an email. Its shares gained 3.6% at 12:51 p.m. in New York.
The U.S. Food and Drug Administration also issued an alert on antigen tests, warning on Tuesday that they can produce incorrect positive results. Problems are more likely in populations with low virus prevalence, or when the test is improperly performed, the FDA said in a statement.
Nursing homes and other care settings have reported false positives from antigen tests, the FDA said. Any type of test is subject to some inaccuracies, and it’s important to follow instructions for antigen testing, confirm results when needed and consider the likelihood of a false positive when looking at results, the agency said.
Antigen tests detect unique protein markers on the surface of SARS-CoV-2. They don’t require heavy-duty laboratory equipment and can produce results in 15 minutes and at a fraction of the cost of PCR tests.
That would make them ideal for places like schools -- but young people in general are less likely to have Covid symptoms. Though federal officials have given the go-ahead for broad use of the tests, they were only cleared by U.S. regulators for use in symptomatic people, based on research in that population, state officials note.
Louisiana, battered by back-to-back hurricanes this fall, was an early recipient of antigen tests from the U.S., receiving about 305,000 to date. Lack of clarity about the tests’ capabilities has left the state in a gray area, said Joseph Kanter, interim assistant secretary for the state’s Office of Public Health.
“On the one hand, we have technology and testing platforms like this one which are new and likely valuable. And everybody has an interest in getting them to people that could benefit from them as quick as possible,” he said. “On the other hand, we don’t have great data on them yet.”
The Oregon Health Authority also recommends against using BinaxNOW to screen asymptomatic people without risk factors like a Covid-19 exposure, citing accuracy concerns. However, the authority doesn’t recommend confirming positive antigen test results with PCR, saying that both are subject to inaccuracies.
Other makers of antigen tests include Quidel Corp and Becton Dickinson and Co. Concerns about antigen tests’ accuracy arose earlier after the U.S. sent thousands of tests to nursing homes nationwide.
The lingering questions are complicating a U.S. government push to distribute antigen tests more widely. Most states are implementing policies similar to Louisiana’s that recommend PCR testing for screening asymptomatic people, Engel said.
As tests are rolled out in places that don’t normally perform them, users may make mistakes, he said. States may change their approaches as more data becomes available, he said.
Louisiana is shipping tests to colleges, school-based health centers, primary care clinics, urgent-care centers and the corrections department, among other locations, according to Kanter. The state expects to receive 1.4 million of the tests in total.
The health department’s guidance doesn’t completely rule out using antigen tests in asymptomatic people. PCR assays should be used to confirm antigen results in certain situations, such as when someone with Covid-like symptoms tests negative or an individual without symptoms or a known Covid-19 contact tests positive, health officials said.
Louisiana has used Abbott antigen tests to screen workers involved in the response to Hurricane Laura, Kanter said. Overall, the tests’ performance was in line with expectations, and no formal studies of them are planned, he said.
Brett Giroir, an HHS official who leads the administration’s Covid-19 diagnostic testing efforts has played down concerns about false results from antigen tests.
“We do support asymptomatic testing being used,” with antigen tests, he said at an Oct. 26 media briefing. “That is the only way that you’re going to screen millions of people a month.”
Using antigen tests for one-off screenings raises the chance of missing infections, especially early ones, said Mark McClellan, director of the Duke-Margolis Center for Health Policy at Duke University, who has been working with the Rockefeller Foundation to develop Covid-19 testing protocols.
But screening individuals regularly with antigen tests, as a partnership between Rockefeller and HHS is doing at pilot sites across the country including New Orleans, can cut down on that risk and allow for quick identification of cases, said McClellan, a former FDA commissioner in former President George W. Bush’s administration. The project will deploy 120,000 Abbott antigen tests and collect data about their performance and how best to use them, including in schools.
Ultimately, though, the tests must still be accompanied by other measures like masking and social distancing.
“For people looking to one-time use of Covid antigen tests as a way to go back to normal, we’re not in that situation now,” McClellan said. “This is one more layer of protection as we try to reopen and get through the rest of the pandemic.”
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