About 8.6 million people live in these areas. Darker areas show where more people live far from hospital care. What will they do as the coronavirus hits?

Even though there are about 5,250 of these acute care and critical access hospitals in the United States, in large areas of the country it is hard to reach one.

This map shows everywhere outside a 30-minute drive from the nearest hospital offering the kind of inpatient medical care needed to treat coronavirus.

As the coronavirus outbreak spreads into rural parts of the United States, more people who live far from a hospital are increasingly likely to need one. That poses challenges for communities where hospitals are scarce and I.C.U. beds are in short supply — even a relatively small outbreak there could overwhelm medical resources, with potentially grim consequences for public health.

Research shows people are less likely to seek health care, even emergency care, when they need to travel farther to get it, especially when they are more than about 30 minutes from a hospital.

“We already know that people in rural regions who are located farther from health care use care less and generally have worse outcomes,” said Dr. Paul Delamater, a researcher on health care access at the University of North Carolina.

And that’s under normal circumstances. In a pandemic, the problem is twofold. Without a hospital nearby, those who are sick may not seek care at all, leaving them to suffer and to risk spreading the infection to others.

But if a large outbreak does occur and too many people need treatment, rural hospitals could easily be overwhelmed and be forced to send patients traveling even farther from their homes for care.

“I would imagine things are only going to get worse, not better,” Dr. Delamater said.

Read more: Closed Hospitals Leave Rural Patients ‘Stranded’ as Coronavirus Spreads

Dozens of rural hospitals have closed in the last decade, many of them in the Southeast. In the West, there have been fewer closures, but hospitals are more dispersed and many are designated “critical access hospitals,” with 25 or fewer inpatient beds. That means fewer beds, farther apart for the sick, whether those with coronavirus or those needing other treatment.

The problem of distance is further compounded by demographics. Rural populations generally tend to be older and have higher rates of underlying health conditions, making them most at risk of hospitalization from the coronavirus.

People living outside a 30-minute drive from the nearest hospital Rank State All ages Rank State 65 and older 1 California 794,000 1 California 151,000 2 Florida 551,000 2 Washington 112,000 3 Arizona 541,000 3 Florida 111,000 4 Washington 537,000 4 Arizona 106,000 5 Missouri 347,000 5 Oregon 82,000 6 Texas 347,000 6 Missouri 75,000 7 Colorado 343,000 7 Texas 75,000 8 New York 331,000 8 Virginia 69,000 9 Oregon 326,000 9 New York 66,000 10 Virginia 325,000 10 North Carolina 63,000 By The New York Times · Source: 2014-18 American Community Survey

Alpine County, which straddles the Sierra Nevada in Northern California, is one of more than 700 counties nationwide with no hospital at all. The closest is in South Lake Tahoe, a 30- to 40-minute drive for most residents, according to Nichole Williamson, the county’s director for Health and Human Services.

Just one person in the county has tested positive for coronavirus so far, but if the outbreak were to grow, Ms. Williamson said, there would not be much they could do. A shortage of medical personnel means that setting up a temporary hospital would not be an option. “We have plenty of buildings we could use,” she said, “but we don’t have the staff to open up an alternate care site.”

Ms. Williamson said that if an outbreak occurred in Alpine County, she would expect people would need to be sent to a bigger hospital in Reno, Nev., about an hour and 15 minutes away.

In some cities where hospitals are overwhelmed, more people have been found dead at home. Evidence is also building that people who might have otherwise gone in for conditions unrelated to the coronavirus are avoiding hospitals for fear of contracting the virus.

So far, those outcomes are a risk but not yet a reality in most rural areas. In some counties with the largest populations living far from hospitals, local officials said they had not heard of anyone failing to get the medical treatment they needed.

In Whatcom County, Wash., for example, 38,000 people live 30 or more minutes from St. Joseph Medical Center in Bellingham. Cindy Hollinsworth, an expert in communicable diseases at the county health department, said that even though many residents did not live within that range, all lived within a 40-minute drive and had access to emergency medical services.

Read more: Coronavirus Was Slow to Spread to Rural America. Not Anymore.

A spokesman for San Bernardino County, Calif., where there are 24 hospitals but 61,000 residents still live outside the 30-minute range, said the current public health concern there was a shortage of tests for the virus, not hospital beds.

But some areas of the country with large populations living far from hospitals are showing cause for concern. Rural communities in three states where the coronavirus has spread — Arizona, Florida and Washington — are already experiencing strain on their local medical facilities.

Outbreak in Navajo Nation

Across Arizona’s remote landscape, about half a million people live more than a 30-minute drive from the nearest hospital. Access is especially difficult in Native American tribal areas, where coronavirus cases are growing quickly.

An outbreak that began in mid-March had reached 350 infections just in Navajo County as of Thursday morning, with a higher rate of cases per capita than most states.

People living outside a 30-minute drive from the nearest hospital Acute care hospitals Critical access hospitals 1,000 2,000 3,000 4,000 5,000+ people Navajo Nation Kingman 40 Flagstaff 17 Arizona Phoenix 8 Yuma Tucson 50 miles Acute care hospitals Critical access hospitals 1,000 3,000 5,000+ people Navajo Nation Kingman 40 Flagstaff 17 Arizona Phoenix 8 Yuma Tucson 50 miles 1,000 3,000 5,000+ people Acute care hospitals Critical access hospitals Navajo Nation 40 Flagstaff Ariz. Phoenix 8 Tucson 50 miles Acute care hospitals Critical access hospitals 1,000 2,000 3,000 4,000 5,000+ people Navajo Nation Navajo County Kingman 40 Flagstaff 17 Arizona Phoenix 8 Yuma Tucson 50 miles By The New York Times

Anne Newland, who operates primary care clinics across Northern Arizona, said smaller tribal clinics were already reaching capacity and transferring patients who needed intensive care to facilities in Flagstaff and Phoenix.

“In Navajo County, they’re trying to get patients who need a ventilator out,” she said. “Patients from these highly affected areas are able to be transferred down to the valley, but that’s an expense.”

Patient transfers can cost up to $20,000, an overwhelming burden for smaller facilities. “Covid-19 is just a condition that’s challenging everybody,” Dr. Newland said.

She also worries that given the severity of the outbreak, people will be hesitant to travel long distances to hospitals at all.

“It’s not just the distance, it’s that people are afraid,” she said. “And sometimes they need to see their doctor or go into the E.R., and they shouldn't avoid that.”

Fear Among Florida Farmworkers

In rural Florida, hospital access is the most limited in the farm towns of the panhandle and north of the Everglades.

People living outside a 30-minute drive from the nearest hospital Tallahassee Jacksonville 10 50 miles Gainesville 1,000 2,000 3,000 4,000 5,000+ people Acute care hospitals Critical access hospitals 95 Orlando 4 Tampa Florida Immokalee Miami Naples 75 10 100 miles Gainesville 95 1,000 3,000 5,000+ people Acute care hospitals Critical access hospitals 4 Tampa Florida Immokalee 75 Naples Miami 10 Gainesville 100 miles 95 4 Tampa Fla. 1,000 3,000 5,000+ people Acute care hospitals Immokalee Critical access hospitals Naples Miami Tallahassee 10 Jacksonville 50 miles Gainesville 1,000 2,000 3,000 4,000 5,000+ people Acute care hospitals Critical access hospitals 95 Orlando 4 Tampa Florida Miami Naples 75 By The New York Times

The lack of a nearby hospital in Immokalee, a migrant farming town of 24,000 in South Florida, creates health care challenges under normal circumstances and is causing greater concern as the coronavirus pandemic unfolds. As of Friday, 34 confirmed cases had surfaced in the town.

Workers there produce most of the state’s tomato supply. They have called for a field hospital to be set up in town through the Coalition of Immokalee Workers, a labor advocacy and human rights group.

“We’re about 40 minutes to an hour to a hospital, so that's going to be very limiting,” said Lupe Gonzalo, a farm worker and staff member of the coalition.

Farm workers are deemed essential workers, but they lack protective equipment, and for many workers social distancing is impractical.

“The buses they ride on to go to the farms are packed, sometimes with over 40 or 50 people,” Mrs. Gonzalo said. “The workers live in confined spaces — maybe 10 to 15 people in a trailer. So if one person gets sick, many people will get sick.”

Empty Hospitals in Washington State

In Washington State, rural hospitals are seeing problems with too few patients rather than too many. Nonurgent procedures are suspended, and people with chronic conditions are avoiding going to the hospital.

“We are actually seeing people delay care that’s kind of concerning right now,” said Jacqueline Barton True, the vice president of rural health programs at the Washington State Hospital Association.

People living outside a 30-minute drive from the nearest hospital Critical access hospitals Acute care hospitals 1,000 3,000 5,000+ people Three Rivers Hospital Seattle WASHINGTON Spokane Tacoma 90 5 Longview Walla Walla 50 miles Acute care hospitals Critical access hospitals 1,000 2,000 3,000 4,000 5,000+ people Three Rivers Hospital Spokane Seattle WASHINGTON Tacoma 90 5 Longview Walla Walla 50 miles 1,000 3,000 5,000+ people Acute care hospitals Critical access hospitals Three Rivers Hospital WASH. Spokane Seattle 90 5 50 miles By The New York Times

Ms. Barton True said at least six critically ill patients had had to be airlifted from rural Columbia County since the last week of March, an unusually high number, and none of them with coronavirus.

All over the state, rural hospitals that canceled elective surgeries to keep beds open for coronavirus patients have taken a heavy financial hit. On Wednesday, a spokeswoman for the Three Rivers Hospital in Brewster said they had just 51 days of cash on hand.

“The most vulnerable rural hospitals are hardest hit by the inability to generate revenue,” Becky Bennett, a spokeswoman for the state health department, said.

Despite some federal aid, there’s growing concern over whether these hospitals will be able to weather the crisis in the long term. Advance payments from Medicare have helped, Ms. Barton True said, but “that money will have to be paid back in a number of months, and a lot of our hospitals are very concerned about how and whether they’re going to be able to pay that money back.”

While cases are declining in the Seattle area, where the U.S. outbreak first began, they are still rising in some rural counties, such as Douglas, though in far smaller numbers. The state is able to run 21,000 tests for the virus each day, but in Kitsap County and other rural areas, health care providers said they were still being told to prioritize testing for high-risk groups, not everyone who may have symptoms.

Steve Metcalf, a spokesman for the Tacoma-Pierce County Health Department, said it was still possible that hospitals there could face problems with capacity. “When the time comes to reduce social distancing — we are not there yet — we anticipate there could be a bounce in cases at local hospitals,” he said.