Sunday, June 28, 2020

Strategies for beating COVID - Targeted testing and positivity reduction

National Geographic has an essay on Here’s how to stop the virus from winning. Case surges, overrun hospitals, and a second lockdown this summer could deal a heavy blow to the United States. Here’s what we need to turn the tide.

Following is an excerpt.

… Even the best diagnostic tests run the risk of yielding a false positive result, so if a city, state, or nation tests too many random people in the general public, you might end up quarantining the wrong people. Rather than test blindly, the highest priorities should be seeking out individuals who have symptoms of possible COVID–19 disease as quickly as possible and processing their tests faster, so the right cases can enter quarantine sooner. That’s how places like New York, South Korea, and the European Union beat back their outbreaks.

“I am deeply worried about approaches that assume we are going to test people who either have no symptoms or no epidemiologic criteria for testing,” says Jennifer Nuzzo, an epidemiologist who leads the Johns Hopkins Testing Insights Initiative at the Center for Health Security.

Nuzzo wants more than three million tests per week to root out COVID–19 from the most at-risk populations, such as by instituting universal and regular testing at nursing homes, prisons, and jails. But 30 million tests per week would be impractical, she says, because there are only so many labs in the country that can process the samples.

“To me, if we have to do that level of testing, it represents a bit of a failure … because that will mean that we have let the epidemic grow to the point where it’s just wildly uncontained,” she says.

The better benchmark for monitoring progress, she says, is test positivity, or what percentage of tests come back positive. The World Health Organization recommends that before places reopen, they need to record a test positivity percentage below 5 percent for at least 14 straight days, as many countries with subsiding outbreaks have done. When places go above this line, it becomes harder to keep COVID–19 from hopping from group to group. Too much positivity can also mean an outbreak is expanding uncontrollably, and because medical centers tend to prioritize patients with the most serious symptoms, more of the milder cases will go unnoticed, worsening the spread.

But rather than follow the World Health Organization’s benchmark, which was decided by an international panel of top experts, the CDC and the White House said that states can start reopening after falling below 20 percent test positivity. “It’s outrageously high,” Nuzzo says. Of the 30 states with cases surging right now, 16 have test positivity rates above 5 percent, and others in this unfortunate group are trending upward too.

Closer to home, all that is true of Pima County. In my analyses, positivity has been in the 10–15 range over the last couple of weeks. And yet we are opening up, that is, opening ourselves to more pain and suffering.

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