The latest coronavirus surge is reaching into the nation’s last untouched areas

Few places would seem better able to ride out an infectious-disease pandemic than Petroleum County, Mont., whose 500 people spread over 1,656 square miles, much of it public lands and cattle ranches. For most of this year, it did just that, becoming the last county in the state and one of the final few in the nation to have logged no cases of the novel coronavirus.

Then came October. Three residents tested positive, knocking Petroleum off zero-case lists, forcing the county's lone school to close for a week and proving, as Sheriff Bill Cassell put it, that "eventually we were going to get it," and that the virus "ain't gone yet."

That is a lesson people in many other wide-open places have been learning as the coronavirus surges anew. Months after it raced in successive waves along the nation’s coasts and through the Sun Belt, it is reaching deep into its final frontier — the nation’s most sparsely populated states and counties, where distance from others has long been part of the appeal and this year had appeared to be a buffer against a deadly communicable disease.

In Montana, which boasts just seven people per square mile, active cases have more than doubled since the start of the month, and officials are warning of crisis-level hospitalization rates and strains on rural health care. In Wyoming, which ranks 49th in population density, the National Guard has been deployed to help with contact tracing. Those two states, along with the low-density states of Idaho, North Dakota and South Dakota, now have some of the nation's highest per capita caseloads. Even Alaska, the least-crowded state, is logging unprecedented increases, including in rural villages.

"People here make the joke that we've been socially isolating since before the state was founded," said Christine M. Porter, an associate professor of public health at the University of Wyoming. "In terms of the reason this happened now and it didn't happen before, it was essentially luck-slash-geography. It's a disease that spreads exponentially once it's taken root, unless you take severe measures to stop it."

The bulk of these states' cases are clustered in their relatively small cities, but infections are fanning out. In Montana, about 55% of cases were in population centers by mid-month, down from nearly 80% over the summer. And although the caseloads may look low, they loom large for local public health officials and facilities.

Sue Woods directs the Central Montana Health District, a Massachusetts-sized area that includes Petroleum and five other rural counties. The district has about 120 active cases, and Woods is working 10- to 12-hour days, mostly on contact tracing.

"The numbers of cases that we see are so small compared to large population centers, but when you take our population into account, we're right in the same percentages," Woods said. "Two of us are doing the bulk of the patient contacts. It is overwhelming."

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Some officials point to the positive side of being hit by the coronavirus later in the pandemic. It gave jurisdictions and health-care facilities the opportunity, they say, to collect personal protective equipment, ramp up testing and learn more about the virus and how to treat covid-19, the disease it causes.

"Up until a few weeks ago, we had been very successful in limiting transmission," said Alexia Harrist, Wyoming's state health officer and state epidemiologist. "It did buy us very important time to be better prepared for this surge."

But with that delay came another risk, others say. As the virus rolls through regions that for months felt relatively sheltered from the disease but not the broader effects of shutdowns and shortages, there is concern that weariness will stymie efforts to stunt the spread. Wyoming, like the Dakotas and Idaho, has no statewide mask mandate, and leaders in the red states have expressed no interest in implementing them.

At a recent news conference, North Dakota Republican Gov. Doug Burgum pointed to a slide showing alarming test positivity rates for states in the upper Midwest and eastern Rockies. North Dakota's hovers around 10%.

"This chart would have been quite boring" until the surge began in September, Burgum said. "Perhaps that gave us a sense of complacency, or maybe a sense of invulnerability, or even a sense of pride that we were somehow going to avoid this thing."

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But now, Burgum warned, the state was on track to add 504 deaths by Christmas.

Deer Lodge County, Mont., swung between two and 10 active cases for much of the summer. An early September outbreak at a correctional facility did not fuel community transmission, and by mid-month, it looked like "maybe we were going to keep dodging the bullet," said Leigh Ann Holmes, health director for the southwestern county, home to about 9,100 people.

That hope vanished after a wedding was held without required county approval. About 200 people gathered for a reception in a barn, Holmes said, and several ended up with the coronavirus, including teachers and employees at the hospital, where earlier this month 10 staffers were out sick. Within two weeks, Holmes said, the county had 80 new cases. The county's schools switched to online learning for two weeks.

In the small county seat of Anaconda, the cases had an outsized effect on the workforce, Holmes said. One person sickened was both an administrator at the middle school and a server at a restaurant; the restaurant had to close temporarily. Several other businesses also did, because of ill or self-quarantining workers or as a precaution.

Among them was the Ranch Bar, founded 50 years ago by manager Eric Hempstead's late grandmother. Hempstead, 28, said he had gotten used to hearing his regulars, many retirees, dismiss the virus as "a bunch of crap that was never really going to come here." Hempstead said he didn't agree, and he abided by state-mandated capacity limits and urged patrons to wear masks, with middling success.

The bar hosted a small wedding reception outside in September, but Hempstead said a group of tourists showed up, and then it got cold outside, and everyone — more than the bar's 38-person limit — migrated inside. Hempstead tested positive for the coronavirus not long after.

Hempstead closed the bar for two weeks, because staffing would have been difficult and also because he worried about his bartender, who's in her 80s, and his customers.

"These people were here when I was 2 years old, crawling under the bar stools," Hempstead said. "Now that they're all older and I'm in charge, I couldn't put any of those people at risk."

Hempstead reopened the bar Oct. 15 — with, he hopes, more authority to demand that customers wear masks. He has little doubt they will keep coming: Snow is already falling, narrowing outdoor options.

"The world gets a lot smaller in the winter in Montana," Hempstead said.

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With flu season looming, that worries Jim Murphy, Montana's chief epidemiologist. As many small and large hospitals fill up and local health officials buckle under caseloads, regional cooperation — combined flu vaccination drives, for example — is shrinking, he said. The major hospital in the hot spot of Billings has had to transfer some Wyoming patients back to their state. Tribal areas have asked the state for contact tracers and ambulance drivers.

"There's no area in Montana that's untouched. It means that every area in Montana now needs to utilize their own resources to respond," Murphy said. "They're not able to help their neighbors."

In central Montana, Woods said she has been able to offload some work, such as immunizations, to a county health office. But she said she is worried about influenza season. Even planning flu shot drives is a challenge because they will have to be indoors.

Petroleum County avoided the coronavirus for so long in part because it's not on a main road, making it even more of an island than other rural counties, Woods said. Its three cases were traced to excursions beyond county lines, she said.

Those cases and others in the region have served as a wake-up call, said Megan Spry, whose job as district sanitarian involves enforcing a state mask requirement at businesses in counties with more than four active cases.

"We had a lot of pushback with masks until covid has become pretty prominent in the area," Spry said. "It took a death happening or a major outbreak before people actually took it serious."

During all the months Petroleum had zero cases, officials did not sit on their hands, said Sheriff Cassell, who is also the county manager and an emergency medical technician on the county's two-ambulance fleet.

The county used federal money to put up plexiglass barriers and create a community telehealth room at the courthouse in the county's only town, Winnett. It distributed masks and hand sanitizer. Cassell said he knows every county resident, and he encouraged them to be cautious.

"You go to the store, and a lot of people aren't afraid of it. Central Montana is a pretty independent part of the United States," Cassell said. "I've just tried to educate people: Try to be cognizant of other people. Maybe you don't care if you get it, but that doesn't mean everyone else wants it."

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Although locals have mostly been spared from the coronavirus, the pandemic has taken a toll, Cassell said. His department has fielded triple the normal number of emergency calls this year — about car accidents, heart attacks and city folks "getting drunk and stupid" and hurt while camping in the county, he said.

Cassell chalks it up to what he calls "corona-crazy." And he says it has stressed Petroleum's emergency crews, who have learned to suit up in protective equipment and fear exposure even in a county with few cases.

"It was inevitable that it was going to get here, and when it did, it was going to spike up real hard," Cassell said of Montana and the virus. "Coronavirus itself didn't get to Petroleum County real bad, and hopefully it doesn't. But the stress and the mental fatigue that comes from dealing with it, we aren't exempt from that."

The Washington Post’s Jacqueline Dupree contributed to this report.