More than 6 in 10 Americans live in counties where people have died of the disease caused by the coronavirus, and about 95 percent live in places reporting at least one case, according to a Washington Post analysis of data compiled by Johns Hopkins University.

At the population level, in other words, the virus is almost literally everywhere, turning the epidemic into a crisis directly affecting the lives of nearly every single person in the United States.

The first coronavirus case in the United States was confirmed on Jan. 20 in a man in Snohomish County, Wash., who had recently visited the epicenter of the global pandemic in Wuhan, China. In just over two months, the virus has spread to more than 2,000 counties representing at least 95 percent of the U.S. population, according to tracking data maintained by Johns Hopkins.

March 13 marks an inflection point in the virus’s spread. That day, it was reported in counties representing more than half the population. Coincidentally, it was a day after Americans woke up to news of travel restrictions on Europe, the cancellation of March Madness and Tom Hanks’s covid-19 diagnosis in Australia.

The virus continued its rapid spread to new segments of the population until about March 21, when confirmed cases reached counties representing 80 percent of Americans. Since then the rate of county-level exposure has slowed somewhat, if only because the virus is running out of new population centers to infect.

As of March 30, nearly every county in the United States with a population of 100,000 or more is reporting at least one coronavirus infection.

These numbers come with caveats. The virus is almost certainly already present in a number counties where no cases have yet been confirmed via testing. Many people who become infected show no or only mild signs of infection, so they may not seek testing. In many regions of the country, there still aren’t enough tests for every potential patient.

Nevertheless, it’s instructive to see where the virus has not yet been reported. The map above, in which counties with no confirmed cases are in orange, is essentially an inverse population map. The orange counties are some of the least populated in the United States, including the wide belt of sparsely populated counties in the central plains.

These counties represent well over half the country’s land area, but only about 5 percent of its population. Their lack of cases illustrates an obvious but easy to forget point: The virus has a harder time spreading in places with fewer people. Density is one of cities’ great strengths, but during a pandemic it becomes a weakness, allowing an infection to spread rapidly among a tightly packed population.

It’s worth pointing out that while rural counties may be remote, they are not necessarily isolated. People living in these places often routinely travel to cities and towns to shop, receive health care and visit friends and family. Rural areas pride themselves on self-sufficiency, but they are nevertheless connected to the rest of the country via travel and trade.

Some rural areas, particularly vacation and second home destinations, are growing concerned at the prospect of city-dwellers fleeing to the country to ride out the pandemic, potentially bringing the virus with them. Many rural counties lack hospitals, making health care access a challenge even in normal times.

If city transplants cause a coronavirus outbreak disproportionate to the availability of hospital beds in a rural area, the results could be catastrophic.

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