NEW YORK (NYTIMES) - It began last month with a trickle of coronavirus infections as college students arrived for the fall semester. Soon that trickle became a stream, with campuses reporting dozens, and sometimes hundreds, of new cases each day.

Now that stream feels like a flood. In just the past week, a New York Times survey has found, US colleges and universities have recorded more than 36,000 additional coronavirus cases, bringing the total of campus infections to 88,000 since the pandemic began.

Not all of those cases are new, and the increase is partly the result of more schools beginning to report the results of increased coronavirus testing.

But The Times survey of 1,600 institutions also shows how widely the contagion has spread, with schools of every type and size, and in every state, reporting infections.

Public health experts say the rising number also underscores an emerging reality of the pandemic: Colleges and universities have, as a category, become hot spots for virus transmission, much as hospitals, nursing homes and meatpacking plants were earlier in the year.

"This is completely predictable," said William Hanage, associate professor of epidemiology at Harvard's T.H. Chan School of Public Health, adding that he and his peers have been "talking to each other since July, if not before, about what's going to happen when the colleges open up."

Universities have struggled financially since March, when the threat of the virus forced students to disperse for their safety.

Hoping to salvage some sense of normalcy - along with lost revenue from housing fees and out-of-state tuition - many schools have invested heavily in health measures to bring back at least some students to campus with the promise of in-person classes and independent living in dorm rooms.

Those plans have been fluid, however, as outbreaks have forced course corrections at campus after campus. It has been sobering, college administrators say, to realise how quickly the virus can spread from a few index cases to dozens or even hundreds of students who have been exposed, if not infected.

The State University of New York at Oneonta sent students home after the virus spun out of control in less than two weeks, with more than 500 cases.

Notre Dame opened in-person classes for its 12,000 students on Aug 10; eight days into the semester, after cases soared, it moved classes online for two weeks and hired security personnel to ensure compliance with quarantine rules. It has now resumed in-person teaching.

Since the beginning of the pandemic, only about 60 of the campus cases have resulted in death - mostly of college staff members - and only a small number have resulted in hospitalisations. But what has happened on campus hasn't stayed on campus.

A New York Times review last weekend of 203 "college town" counties where students comprise at least 10 per cent of the population found that about half had experienced their worst weeks of the pandemic as students returned in August, and about half of those were experiencing peak infections this month.

Even schools with state-of-the-art mitigation plans have been challenged by outbreaks. The University of Illinois at Urbana-Champaign, for instance, imposed a lockdown last week after a sharp uptick in cases, even though the college requires its 40,000 students to take coronavirus tests twice a week.

Over the past week, case counts have continued to grow at the University of Nebraska-Lincoln - even as the university has suspended several fraternities and sororities for parties - and nearly doubled at the University of Missouri in Columbia, which added more than 540 cases, according to the campus newspaper.

At California State University Chico, which allowed only a small fraction of students to return to campus, cases rose by more than 60 per cent - even though the last of its in-person classes had been cancelled and its dormitories housed only a handful of needy students.

About 14 per cent of Illinois State University's 1,300-plus cases have been added this week.

Schools have scrambled, hoping to contain outbreaks until Thanksgiving, when most students are scheduled to go home until next year or pivot to remote instruction.

Texas Christian University postponed the opening game of its football season. The University of Wisconsin-Madison paused its in-person classes. The University of Alabama has started randomly testing 3 per cent of the campus population weekly and has penalized more than 600 students for violating a ban on gathering on or off campus, suspending 33 students.

But Alabama, whose Tuscaloosa campus has suffered one of the nation's more significant college outbreaks, has not opted to repeatedly test the entire student population, unlike some other schools where the virus is spiking. Hanage cautioned that few campuses will make it through the semester with in-person classes without rigorous screening.

At the University of Dayton in Ohio, President Eric Spina said the school of 8,500 undergraduates launched an aggressive testing and tracing program after a meeting of students with too few masks caused a cluster of cases, followed by another outbreak in dense student housing on the campus periphery.

That level of testing, however, has been the exception. A group of faculty and students at the California Institute of Technology who in August analysed reopening plans at some 500 universities around the country found that only 27 per cent of schools planned to test undergraduates for the virus as they returned to campus, and only about 20 per cent planned to do any regular screening.

An author of the study, Sina Booeshaghi, a Caltech graduate student, said that the extent of a campus's testing program correlated strongly with the size of its endowment, indicating that cost was a factor. (Coronavirus tests can cost US$100 or more per person.) Lior Pachter, a computational biologist at the university, said many schools had pushed responsibility for health and safety down to the individual student or faculty level.

At Miami University in Oxford, Ohio, officials said they had no plans to alter their existing protocol when dorms opened next week for 5,000 students, most of them freshmen. The school has recorded more than 1,174 cases since Aug. 17 - about half of those in the past week - even though classes started remotely and residence halls have been closed. The school plans to offer in-person classes starting Sept 21.

So far, the university has recorded no hospitalisations or deaths among students, a university spokeswoman said. Still, some in the community are nervous.

"Everyone goes to the same places in Oxford, and I don't think the students are careful," said Megan Bernstein, 47, who said she had grown up in the town and was there to visit her father.

Trenton Jordan, 21, a junior, agreed. "Probably 99.99 per cent of the people, when they go to an off-campus party, aren't wearing a mask," he said. "Most college kids are not worried about the virus."

In Springfield, Missouri, David Hinson, executive vice president of Drury University, said he has wrestled with whether to send students home should infections there continue rising. They spiked after school started in August, and he expects they may spike again now, after Labor Day. Most of Drury's 1,416 undergraduates live within three hours of campus and so could have left the campus bubble to go home over the long weekend.

Drury currently has about 30 active cases, but its cumulative total - now about 85 cases - has steadily risen. About 875 students are living on campus this fall, in single rooms, down from 1,090 in a normal year. All classes are being held in person, but Hinson said that as far as he knows, no one has been infected in the classroom. The risk, he said, is greater in the dorms.

Lacking guidelines from the state, the university worked with the local health department and decided that it would look for outbreaks from class to class and put those classes online for two weeks, rather than shutting down the entire school. No classes have been shut down so far, he said.

California State University Chico, like the rest of the California State University system, had thought it wouldn't have to weigh such fine-tuning. The school announced in May that it would hold more than 90 per cent of its fall classes remotely and cut back dramatically on the number of students who would be living in its already limited campus housing.

But the school still allowed some 2,500 of its 17,000 students to take classes on campus and housed about 750 students in dorms. By August, infections had begun to spike, many among students living off campus.

Since then, infections have continued to rise, driving increases in the surrounding community and county. The university's president, Gayle Hutchinson, isn't counting on things returning to normal any time soon.

"We gave it our best shot," said Hutchinson in a news conference announcing her decision to move all but about 100 students off campus and end the remaining in-person classes. "Maybe everything will have to remain virtual until we have a vaccine."