For the first time since early August, the number of newly reported coronavirus infections in the United States on Thursday topped 60,000. More than 36,000 people are hospitalized nationally with covid-19, the disease caused by the virus, amid a long-feared autumnal rise of infections and serious illnesses.

This is not a regional crisis, but instead one that is intensifying almost everywhere in the country. Forty-four states and the District of Columbia have higher caseloads than in mid-September. The virus is spreading in rural communities in the heartland, far from the coastal cities hammered early in the pandemic.

Wisconsin set a record Thursday when it surpassed 4,000 newly reported cases. Illinois also reported more than 4,000 cases, eclipsing records set during the state’s first wave in April and May. Ohio set a new high, as did Indiana, New Mexico, North Dakota, Montana, and Colorado. In El Paso, officials have ordered new restrictions and lockdowns amid a frightening coronavirus surge.

“We know that this is going to get worse before it gets better,” Wisconsin Department of Health Services secretary-designee Andrea Palm said at a briefing Thursday. “Stay home. Wear a mask. Stay six feet apart. Wash your hands frequently.”

Some hospitals in the Upper Midwest and Great Plains have become jammed with patients and are running low on intensive-care-unit beds. On Wednesday, Wisconsin opened a field hospital on the grounds of the Wisconsin State Fair Park outside Milwaukee and will eventually be able to treat more than 500 patients.

Montana reported a record 301 hospitalized covid-19 patients Thursday, with 98 percent of the inpatient beds occupied the day before in Yellowstone County, home to the city of Billings and the state’s most populous county.

During the past week, at least 20 states have set record seven-day averages for infections, and a dozen have hit record hospitalization rates, according to health department data analyzed by The Washington Post.

After a midsummer spike in the Sun Belt, the country registered a decline in cases in August that bottomed out over the Labor Day weekend — but at a level that experts said was still dangerously high, around 40,000 new cases daily. The reopening of many schools and colleges did not immediately lead to a major spike in cases, as some experts had feared, but the numbers have steadily crept upward.

The increase in cases and hospitalizations since late August has been followed by a more modest rise in covid-19 deaths. That could reflect, in part, improved patient care from battle-tested medical workers. The widespread use of powerful steroids and other treatments has lowered mortality rates among people who are severely ill.

But epidemiologists have repeatedly cautioned that most people remain susceptible to the coronavirus and transmission is likely to be facilitated by colder weather. Not only do people spend more time indoors, but the dry indoor environment is congenial to the spread of respiratory viruses.

On Oct. 3, the national case count surpassed 50,000 for the first time since summer. As more data arrived Thursday from health departments, it became clear that the 60,000 milestone would be reached for the first time since Aug. 7, when infections were widespread in the Sun Belt. By late Thursday the daily total of more than 63,500 cases represented the highest number since July 31.

The cumulative number of cases in the United States since the start of the pandemic is likely to surpass 8 million on Friday, according to The Post’s analysis. The official death toll stood just shy of 217,000 late Thursday.

“Inevitably, we’re moving into a phase where there’s going to need to be restrictions again,” said David Rubin, director of PolicyLab at Children’s Hospital of Philadelphia.

Whether this represents a second wave or even, considering the summer Sun Belt spike, a third, is a matter of semantics. The message from infectious-disease experts is clear and emphatic: The virus isn’t going away magically, and everyone needs to prepare for a challenging winter.

This week, the Centers for Disease Control and Prevention updated its advice on how people should handle the upcoming holidays, saying people at elevated risk of a severe covid-19 illness — older people and those with chronic conditions — “should not attend in-person holiday celebrations.”

That unhappy message reflects the concern among epidemiologists about household transmission and the tendency for people to lower their guard around individuals they know best. CDC Director Robert Redfield said this week in a conference call with governors that Thanksgiving celebrations could spark high viral transmission rates, according to a recording obtained by CNN. “What we’re seeing as the increasing threat right now is actually acquisition of infection through small household gatherings,” Redfield said.

Among those taking a cautious approach will be Anthony S. Fauci, the 79-year-old director of the National Institute of Allergy and Infectious Diseases. In an interview this week with CBS News, he said his three children will not be flying to Washington this Thanksgiving for a family gathering because his advanced age puts him at higher risk. He urged people to consider changing their plans.

“It is unfortunate because that’s such a sacred part of American tradition, the family gathering around Thanksgiving,” Fauci said. “You may have to bite the bullet and sacrifice that social gathering.”

There is no evidence the coronavirus is becoming less lethal through mutations. Colder weather that drives people indoors could have the opposite effect, Rubin warned: People may be exposed to larger amounts of virus inside.

Experts will be watching death tolls closely to see whether rising infection numbers lead, as in the past, to a spike in deaths many weeks later. The nation, however, has a patchwork medical system in which some people and places have much greater access to the best medical care.

Much of the new transmission is taking place in rural communities in the heart of the nation with limited hospital capacity. They also tend to have older populations more vulnerable to severe outcomes from covid-19.

The effects of the coronavirus have been strikingly pronounced in recent weeks in Republican-leaning counties, according to a new analysis of health data from Harvard University researchers that compares the latest number of cases and deaths to county-level voting patterns in the last presidential election.

The research, which has not been peer-reviewed, shows that “red” counties with the most intense leanings toward Republicans have had the largest recent increases in cases, while “blue” counties that lean Democratic have tended recently to be flat.

“The redder it is, the more it goes up. The bluer it is, the more it stays flat,” said Nancy Krieger, an epidemiologist at Harvard’s T.H. Chan School of Public Health and lead author of the paper.

The Harvard professors suspect that the Republican-leaning communities have been less inclined to follow public health guidance, including recommendations about mask-wearing and social distancing. The collision of the pandemic with election-year politics has had ripple effects that have undermined the collective response to this health crisis.

“Actions to suppress the transmission have been stronger in blue states than in red states, and the virus has run its natural course,” Harvard epidemiologist William Hanage said.

Many of the country’s leading medical experts, including top federal government doctors, have urged adherence to public health guidelines, but that message has competed with the pronouncements of President Trump and his closest political allies, who have played down the threat of the coronavirus.

The stark conflict in those messages was amplified this week when a senior administration official said the White House strategy for fighting the pandemic is bolstered by the Great Barrington Declaration, a document posted online by three “dissenting scientists” that argues the virus should be allowed to spread at natural rates among younger, healthier people while older people and others who are vulnerable are kept isolated.

Geography, demographics and chance could play a role in the recently observed spike in many Republican-leaning counties. They are often rural and remote from the big, Democratic-leaning cities first hit by the virus. In some of those places, the virus may only recently have seeded itself, carried by travelers from areas with higher transmission.

Ali Mokdad, an epidemiologist at the University of Washington’s Institute for Health Metrics and Evaluation, reviewed the Harvard report and said it generally matched what the institute has seen in its modeling of the pandemic. Mokdad offered a simple explanation for why rural places might be seeing so much transmission this late in the pandemic.

“When covid-19 came in the United States, it didn’t show up immediately in rural communities,” he said. “And then people in these communities felt, ‘That’s not us, that’s the big cities.’ They let down their guard.”

He added, “It’s eventually going to spread everywhere in the U.S. … This virus is opportunistic. We make a mistake, that virus will win.”

Rubin, the PolicyLab director, predicted that some big cities, including Chicago and Denver, are also poised to see a surge in cases in coming weeks. And he warned against associating viral transmission with partisanship.

“There may be some differences between these counties, but let’s not overstate them. This is not a binary issue of less safety in Republican versus Democratic-leaning counties. The truth is that pandemic fatigue and lapsing vigilance is more universal than this [Harvard] article suggests,” Rubin said in an email.