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Tests alone won’t stop COVID-19 from spreading

Testing wasn’t enough to spare the White House and may not work in schools and other places

by Megha Satyanarayana
October 13, 2020


An image of President Trump at a rally in Florida.
Credit: Associated Press
President Trump appears at a rally after his doctor says he has tested negative for COVID-19 on consecutive days.

After avoiding questions as to President Donald J. Trump’s COVID-19 status, the president’s doctor, Sean Conley, says the president has tested negative for consecutive days using a rapid test from Abbott that the Trump administration plans to send to governors all over the US.

Trump’s negative tests are the latest chapter in a drama that began Oct. 2 when he announced on Twitter that he and First Lady Melania Trump had tested positive for COVID-19.

As more people in Trump’s inner circle revealed positive COVID-19 tests, the White House at first refused to do any contact tracing related to a recent Rose Garden event where it was suspected the virus had been spread from person to person. At the event, celebrating the nomination of Amy Coney Barrett to the Supreme Court, few people wore masks, and the guests mingled in close proximity.

No masks. No social distancing. Constant testing.

This has been the White House’s strategy to stave off COVID-19, and test results, again, appear to be the metric by which the president is resuming public appearances. Experts tell C&EN that this approach is flawed from the outset.

SARS-CoV-2 can take several days to multiply to detectable levels by diagnostic tests. Some diagnostic tests are not as reliable as others. Relying on negative tests in a system where some percentage of tests will be wrong means that some sick people could seed an outbreak. It’s particularly risky to rely on tests when many people who are infected show no symptoms, either for the first several days, or for the entirety of their illness.

According to Conley, Trump tested positive for COVID-19 on Oct. 1. The CDC says that to prevent further infections, people may need to isolate for up to 20 days depending on the severity of their disease. In the first days after his diagnosis, Trump was treated with an experimental monoclonal antibody therapy, an antiviral, and oxygen and steroids, both of which are typically reserved for people who are seriously ill. According to pool reports, he left for a Monday rally without a mask on.

“Every single person has a different level of exposure, time of exposure. Testing is just one arm of the way to fight COVID in any given setting, and even if you have the perfect test, the best test that we could use, you still need to wear masks. You still need to socially distance,” says Joseph Petrosino, an infectious disease expert at Baylor College of Medicine.

The president and his inner circle appear to have done neither.

Conley said that Trump’s infection was first detected with a rapid test and then confirmed by a technique called polymerase chain reaction, or PCR, a multistep process by which genetic material—in this case, genetic material of SARS-CoV-2—is converted into a form that an enzyme copies over and over so it can be easily detected by a machine. PCR is widely considered the most stringent of the diagnostic technologies available for COVID-19.

It is also one of the slowest technologies. That means some have turned to faster, but often less accurate diagnostic technologies to do the kind of frequent testing needed to keep open a school district, sports league, or, in this case, the government.

The White House has reportedly been using two rapid diagnostic tests made by Abbott: ID NOW and BinaxNOW. Trump’s most recent negative tests came with the BinaxNOW test, which Conley says has been confirmed by other methods, including viral load and other measurements.

BinaxNOW is a roughly $5 antigen test, meaning it detects a piece of the virus’s proteins rather than its genome. Intended to be given within the first few days after symptoms start, the test is not necessarily meant for daily use. The department of Health and Human Services is sending 150 million of these tests to states “to provide support to K-12 teachers and students, higher education, critical infrastructure, first responders, and other priorities as governors see fit.”

The test detects a chunk of SARS-CoV-2’s nucleocapsid, a protein that associates with the viral genome. Like some pregnancy tests, the lateral flow assay gives a positive or negative result in a few minutes based on colored stripes. According to an Abbott spokesperson, BinaxNOW accurately diagnoses COVID-19 97% of the time. Used as a daily test in a large setting, that 3% fail rate could mean many infections go undiagnosed. And some scientists say the tests have not been well-validated, so that margin of error could be higher.

By contrast, ID NOW looks for a portion of the viral genome that allows it to replicate. It uses a technology called isothermal nucleic acid amplification that is similar to but faster than PCR. While PCR requires several time-consuming temperature shifts to allow the strands of genetic materialto be separated so that they can be copied, and to allow the enzyme that does the copying to work efficiently, isothermal amplification works at a constant temperature.

Abbott says ID NOW, which requires a special machine to perform the assay, can give results in less than 13 minutes. In people tested within 7 days of exhibiting symptoms, an Abbott spokesperson says ID NOW was able to correctly diagnose someone with COVID-19 95% of the time. Similar tests developed by other companies have reported both lower and higher sensitivities.

Petrosino says rapid tests like ID NOW use a type of isothermal amplification that results in a trade-off in speed over sensitivity. PCR is considered the “gold standard” and isothermal amplification is “a process that’s not quite as efficient and robust.”

In a place where cost is not a factor, the molecular tests like ID NOW might be more accurate than the antigen tests for monitoring infections, he says. “If they are being used multiple times a week, let alone daily, then that’s probably the best regimen we can suggest,” he says. “But again, that’s not the only thing you should be doing.”

As scientists and public health officials continue to criticize the Trump administration’s handling of their in-house outbreak, others are praising the way that the National Basketball Association coupled constant testing with social distancing to allow part of the season to be played. Earlier this week, the Los Angeles Lakers won the league’s championship, and there were no outbreaks and few positive infections overall in what many are calling the “bubble experiment.”

The NBA used multiple tests in their regimen, focusing on ones that could diagnose COVID-19 via a saliva sample instead of a nose or throat swab. One of those was Yale University’s saliva test, a PCR-based test that costs less than $5. A saliva sample is treated with an enzyme that destroys proteins, including any that might eat viral RNA. The sample is then heated up to destroy the proteinase, leaving behind the viral RNA for processing via PCR. The NBA also used another PCR test created by Rutgers University.

In the meantime, though, it appears that Trump’s brush with serious illness has minimally changed his behavior, or that of his followers. At his first public appearance since being cleared by Conley, Trump wore a mask, but took it off to speak to a crowd of supporters, of whom few wore a mask.

Within the White House, as longtime staffers fall ill, there are reports that mask-wearing is inconsistent.

“Masks are still not the defacto mode of the day,” Petrosino says of the White House strategy. “Without masks, [that strategy is] broken.”


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