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US Has Not Turned Corner in Shutting Down Coronavirus Nationwide
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Mark Mascolini
"The United States has not yet turned the corner nationwide" in the fight to stop the spread of COVID-19, according to a state-by-state analysis by statistician Nate Silver [1]. That conclusion "would largely be the same with whatever metric I chose," Silver writes, whether newly diagnosed COVID-19 cases, the positive test rate, or number of deaths.
Headline-grabbing US epicenters of the COVID-19 epidemic, like New York and Louisiana, have seen a drop in new cases in recent weeks. But Silver stresses that "in nearly half of all states in the U.S., there are as many COVID-19 cases as ever, and in some cases, even more."
Silver, who heads the fivethirtyeight.com number-crunching group, set out to chart the COVID-19 positive test rate (positive tests/all test results) in all 50 states and Washington, DC. Because the quality of reporting negative test results varies from state to state, Silver developed a 3-step method "to smooth erratic reporting on negative tests," which he details in the article [1]. Then for each state he estimated the positive-test rate for the past 5 weeks-the 7-day periods ending on March 25, April 1, April 8, April 15, and April 22. He took all basic data from the COVID Tracking Project (https://covidtracking.com/).
For 18 states and Washington, DC, the estimated percentage of positive COVID-19 tests met or tied a new high in the latest week (ending April 22). Almost 95 million people live in those 19 jurisdictions. Most states on this list lie in the Midwest, but a string of these states hopscotches up the eastern seaboard from North Carolina to Connecticut. Here are the 19 jurisdictions and their last 2 weekly estimated positive test rates:
Arizona: 10%, 13%
Arkansas: 8%, 9%
Colorado: 24%, 25%
Connecticut: 35%, 39%
DC: 21%, 27%
Delaware: 17%, 22%
Illinois: 23%, 24%
Iowa: 13%, 23%
Kansas: 10%, 14%
Kentucky:13%, 15%
Maryland: 24%, 24%
Minnesota: 7%, 10%
Mississippi: 9%, 9%
Nebraska: 9%, 18%
New Mexico:7%, 7%
North Carolina: 8%, 10%
North Dakota: 3%, 8%
Ohio: 13%, 24%
Virginia: 19%, 22%
The biggest week-to-week jumps lie in 4 Midwestern state: Iowa, Ohio, Nebraska, and North Dakota. Challenges to social distancing explain some persistent increases-for example, prison populations in Ohio and meat-packing workers in Iowa. Social distancing, Silver suggests, "doesn't work for people who can't afford to do it, which means that even in places that seem to be controlling the outbreak, there can still be huge numbers of cases among essential workers."
The analysis pinpoints 6 states where the positive test rate peaked in the week ending April 15: Alabama, Massachusetts, Missouri, Pennsylvania, Rhode Island, and South Dakota. But Silver observes that 5 of these 6 states (all but Alabama) are only a few percentage points off their peak in the week ending April 22. Combining the 18 states in the first group, 5 states in the second group, and a few more states in the remaining group indicates that new COVID-19 cases still stand at or near their peak in half of US states.
Silver also suggests a positive interpretation of these findings: New COVID-19 cases are falling in about half the country, and in much of the rest of the country the positive-test rate is not climbing fast. "The catch here," he adds, "is the spread would likely accelerate again if restrictions were lifted." That experiment is starting right now (April 24) in Georgia, and other states will soon follow.
fivethirtyeight's numbers guru cautions that, while social distancing almost certainly flattened the new-case rate in the United States, that strategy may not bend the curve back down. In statistical terms, the effective reproduction number (R) must lie below 1.0 for the curve to fall and the epidemic to die out. An R of 1.0 means the new-case rate will stay at whatever plateau it set when the increase ended. And an R above 1.0 means the new-case rate will climb again.
Silver opines that social distancing, by itself, "may only be enough to allow us to fight the coronavirus to a draw." Ending the epidemic may require additional measures, like better testing, case tracking, quarantining sick people, and better sanitation and hygiene.
Reference
1. Silver N. Coronavirus cases are still growing in many U.S. states. April 23, 2020. fivethirtyeight.com.
https://fivethirtyeight.com/features/coronavirus-cases-are-still-growing-in-many-u-s-states/
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