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Coronavirus cases in the U.S. have surged in recent weeks but remain comparatively low in lower-income and rural areas, according to a new analysis from The Associated Press.

Among more than 3,100 counties in the U.S., nearly 1,300 had no confirmed cases of COVID-19, data compiled by Johns Hopkins University showed.

Of the counties without positive tests, 85 percent were in rural areas that generally saw less everyday contact between people, which could help transmit the virus.

However, counties with zero positive tests for COVID-19 have had a higher proportion of people older than 60 — the most vulnerable to severe effects of the virus — and far fewer intensive-care beds should they fall sick, The Associated Press reported.

The demographics of these counties held major implications as the Trump administration has developed guidelines to rate counties by risk of the virus spreading, empowering local officials to revise social-distancing orders that have played a role in the U.S. economic downturn.

Infectious-disease experts have noted opportunities to slow the spread of coronavirus in remote areas of the country benefiting from "natural" social distancing and isolation, if initial cases are detected and quarantined aggressively. That could buy time for rural health-care networks to provide robust care and reduce death rates.

But, they also signaled concern that sporadic testing for coronavirus could be masking outbreaks that– if left unattended – might overwhelm rural health networks down the road.

"I hope the zeros are really zeros — I worry that they're not doing enough testing in those regions because they're not thinking they're at risk," said Christine K. Johnson, a professor of epidemiology at the University of California, Davis.

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In New Mexico, where nearly half of the state's 33 counties have been free of any positive coronavirus cases, Gov. Michelle Lujan Grisham, a Democrat, has moved aggressively to contain the coronavirus' spread with a statewide school shutdown and ban on most gatherings of over five people.

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The state is among the top five states in coronavirus testing per capita, though some virus-free counties aren't yet equipped with specialized testing sites beyond samplings by a handful of doctor offices.

The Associated Press contributed to this report.