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August 5, 2020

Why some experts are embracing cheaper (and less accurate) coronavirus tests

Daily Briefing

    The United States' coronavirus testing system is failing to identify and isolate positive cases—and in response, some of the nation's top public health experts are calling for divergent strategies to bolster the impact of testing, with some saying we need to test more people, and others claiming we should test less.

    The 3 biggest questions about Covid-19 testing, answered

    When it comes to coronavirus testing, America still falls short

    Ashish Jha, a general internist and professor of global health at the Harvard T.H. Chan School of Public Health, writes in opinion piece published by TIME that a lot "of the conversation around [coronavirus] testing has focused on accuracy." Jha writes, "The intuition is clear: we want a test that won't miss positive cases and send infected individuals back into the world to spread the virus."

    As a result, polymerase chain reaction (qPCR) tests have become the "backbone of our testing infrastructure," Jha writes.

    However, as Aaron Carroll, a professor of pediatrics at Indiana University School of Medicine and the Regenstrief Institute, writes in a separate opinion piece for the New York Times, these qPCR tests are "uncomfortable," "slow," and "in short supply."

    And due to the short supply and slow turnaround time, providers are often reserving coronavirus tests for the sickest patients, which means the majority of people in the United States are not getting tested. Moreover, those who do get tested often have to wait a long time—between 10 and 15 days—to get their results, Jha writes, "rendering these tests useless as a tool to prevent transmission and bring the pandemic under control."

    In response, Jha, Carroll, and other health experts are brainstorming different ways to conduct coronavirus testing that would detect more cases of infection and curb the virus' spread.

    Jha, Carroll: Test more people—even if that means using less accurate tests

    By prioritizing accuracy, Jha and Carroll in their opinion pieces each contend that the United States is failing to test the majority of people infected with the coronavirus—and undermining the country's ability to quickly test those who are infected. In fact, according to CDC, the United States is currently identifying about one of 10 of coronavirus cases through testing, meaning "the ability to identify and isolate positive cases … is only about 10%," Jha writes.   

    According to Jha and Carroll, the United States should focus instead on testing everyone as often as possible. "[S]tudy after study shows that for surveillance and mitigation, what matters most is the frequency with which we test people, and the speed with which we can act on results," Carroll writes.

    Jha in his opinion piece specifically recommends mass-producing a paper-strip rapid antigen test that Americans can use to test their infection status every day. "If everyone in the United States [was tested] daily, we would dramatically drop our transmission rates and bring the pandemic under control," Jha writes. 

    Jha acknowledges the shortcomings of antigen tests, noting that because they require a higher viral load to identify infection, they can miss positive cases. However, the "frequency of testing and the speed of results counters that concern," Jha writes, explaining that if every American took an antigen test that had a sensitivity of 50%, the country would identify 50% of coronavirus cases, which is much higher than the 10% the country's currently finding. Moreover, because the antigen tests require a higher viral load to identify infection, they would be most accurate at the "peak period of infectiousness," Jha writes.

    Carroll echoes those recommendations, noting that while tests that require nose swabs or saliva—rather than the nasopharyngeal swabs required for qPCR tests—may be less precise, they "could be collected really quickly, in large groups, with minimal supplies." Similarly, "pool tests," which involve testing a pool of samples from patients in areas of the United States where coronavirus cases are not prevalent at once, could also hasten results, he writes. Labs would only have to conduct individual tests if the whole sample tested positive; if it was negative, "you can assume no one person in the pool is infected and move on," Carroll explains.  

    "We have to start accepting less accurate, widespread testing for groups," Carroll concludes, adding, "That's how we minimize risk."

    Similarly, Jha writes, "The evidence makes clear it is time for a paradigm shift on testing. Our goal should be to identify and prevent every cluster and every outbreak of Covid-19."

    Osterholm asks: Should we be testing fewer people?

    But some health experts argue that the percentage of negative tests in the United States and the shortage of testing supplies indicate that we should be testing fewer people.

    According to Vox, about 91.5% of U.S. coronavirus tests come back negative, meaning "there is a good chance many batches will come back without signs of the virus, clearing all of the pooled individuals and freeing up that additional testing capacity for those who need it most."

    As a result, some experts say America needs stricter testing, not broader testing.

    While Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota, agrees that rapid at-home tests "would be tremendously helpful" once they are sufficiently accurate, he asserts that the United States in the meantime must ration coronavirus tests.

    He and his colleagues developed a hierarchy for so-called "smart testing" that would minimize the number of people getting tested amid a shortage of supplies and resources. According to Osterholm, the people who should be prioritized for coronavirus testing, listed in order of priority, include:

    1. Hospitalized patients with symptoms;
    2. Symptomatic health care workers, first responders, essential workers, and those who work in high-risk facilities (like long-term care institutions or homeless shelters);
    3. Symptomatic people in the community; and
    4. People without symptoms who live in high-risk facilities.

    "That's where we're going to get the most bang for the buck," he said, adding that the hierarchy would reduce the number of unnecessary tests conducted in America. "[W]e could do more with the tests that we currently have, which would speed things up—less volume and more high-impact outcomes," he said.

    According to Vox, California has already instituted a statewide hierarchy for coronavirus testing, with the first groups including hospitalized patients and people with symptoms of Covid-19, the disease caused by the virus. People who are asymptomatic but think they might have been infected with the coronavirus are in the last group.

    And several organizations—including Quest Laboratories and LabCorp, which conduct coronavirus testing—have started to stratify testing based on urgency. However, in the absence of widespread rules, Quest labs has also requested that providers prioritize certain high-risk groups for testing "so that we can direct our capacity to patients most in need" and avoid being overwhelmed with tests.

    But Osterholm said if Americans continued to practice physical distancing, wear face masks or coverings, and wash their hands, they could "drive these case numbers down" and the country could test more low-risk individuals. "If we only needed to test one-tenth the number of clinical cases, we can start matching supply with actual need. Right now, our caseload outstrips supply capacity," he said (Jha, TIME, 7/29; Carroll, New York Times, 7/28; Courage, Vox, 7/31).

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