Masked students walk through the campus of Ball State University in Muncie, Ind., Thursday, Sept. 10, 2020. College towns across the U.S. have emerged as coronavirus hot spots in recent weeks as schools struggle to contain the virus. Out of nearly 600 students tested for the virus at Ball State, more than half have returned been found positive, according to data reported by the school. Dozens of infections have been blamed on off-campus parties, prompting university officials to admonish students. (AP Photo/Michael Conroy)

Just two weeks after students started returning to Ball State University last month, the surrounding county had become Indiana’s coronavirus epicenter.

Out of nearly 600 students tested for the virus, more than half have been positive. Dozens of infections have been blamed on off-campus parties, prompting university officials to admonish students.

University President Geoffrey Mearns wrote that the cases apparently were tied not to classrooms or dormitories but to “poor personal choices some students are making, primarily off campus.”

“The actions of these students are putting our planned on-campus instruction and activities at risk,” he said.

Similar examples abound in other college towns across the nation. Among the 50 U.S. counties with the highest concentrations of students and overall populations of at least 50,000, 20 have consistently reported higher rates of new virus cases than their states have since Sept. 1, according to an Associated Press analysis.

On average, infection rates in those 20 counties have been more than three times higher than their states’ overall rates.

At James Madison University in Virginia, which recently sent students home through September amid a surge in cases, the county is averaging a weekly infection rate of nearly 90 cases per 100,000 people, or more than eight times the statewide average.

Health officials fear that surges among college students will spread to more vulnerable people — older ones and those with underlying health problems — and trigger a new wave of cases and hospitalizations. Some worry that colleges could overwhelm hospitals already bracing for increasing cases of COVID-19 and flu this fall and winter.

“There’s this waiting game. Does it stay on college campuses or will it escape?” said Dr. Jeff Pothof, chief quality officer at the University of Wisconsin medical center in Madison, where cases among college students have been climbing.

While universities have emerged as hot spots in nearly every state, many of the worst outbreaks have been scattered across the South and Midwest. Of the 50 college counties analyzed by the AP, James Madison’s had the highest infection rate, followed by counties that are home to the University of Georgia, Florida State and Indiana University in Bloomington.