LOS ANGELES (NewsNation) — With 104 University of Southern California students testing positive for the coronavirus this week, officials on Thursday warned students against holding gatherings believed to be fueling the outbreak.

Of the cases found so far this week, 31 were from testing of asymptomatic people and another 73 were from testing those who have symptoms or had been exposed to an infected person, USC Student Health’s Dr. Sarah Van Orman told NewsNation affiliate KTLA. There have been no reports of students severely ill with COVID-19.

The university has tested around 6,500 students for the virus since Aug. 3.

While Van Orman said the increase is largely attributed to more testing, most infections were contracted through small gatherings like dinners and study groups.

“You really can’t get together with people outside your household, particularly if you’re inside and you’re going to be eating and drinking with your facial coverings off,” Van Orman said. “The infection spreads incredibly easy in those settings.”

There have also been reports of a few large parties taking place, the doctor said.

On Monday, university officials reported an “alarming increase” in cases among students, counting 43 new cases over the preceding seven days, during the first week of the fall semester. Van Orman said the new cases are part of the “same pattern” noted last week.

There were more than 100 USC students ordered to quarantine for 14 days after being exposed to the coronavirus as of Monday. It’s unclear how that number has changed.

USC is holding all classes online and there is no in-person instruction on campus.

There are few students living in the university’s residence halls, and most of those who tested positive for the virus were living in private apartments around USC, Van Orman said.

USC is offering free testing to students and the university strongly recommends weekly coronavirus testing for those living around USC, especially those who have housemates.

In early August, Los Angeles County’s top health official announced a coronavirus outbreak among 45 people at USC was tied to three fraternities.

Many colleges and universities across the country have had to reexamine plans to return to in-person learning amid the pandemic.

In-person undergraduate classes at the University of North Carolina-Chapel Hill were moved online following an increase in the COVID-19 positivity rate from 2.8% to 13.6% at Campus Health, the university announced on Aug. 17.

At the University of Notre Dame in Indiana, undergraduate classes were brought back to online only. Some public spaces were closed and access to dorms was restricted.

NewsNation affiliate KTLA contributed to this report.