Johns Hopkins University on Wednesday announced a two-day suspension of in-person classes for undergraduates on its Homewood campus after it said 30 students recently tested positive for the coronavirus.

Face-to-face classes and other activities resume Friday, the university said.

A preliminary investigation suggests the cluster of cases is linked to off-campus gatherings that were hosted over the weekend, officials said. Many of the students who contracted the virus are athletes, according to a message sent to students.

Students who tested positive have been instructed to isolate themselves from others. The announcement comes about a week into the semester, which started Jan. 25.

“We know this is disappointing news for our community, and we wish to reaffirm our fundamental commitment to the safety of our faculty, staff, students and Baltimore neighbors,” officials said in an email to the campus. “Although this is not the way we wanted to start this new term, we also know that with the proper commitment to our established safety protocols, we will be able to have a successful and safe semester together.”

The campus will continue to investigate the scope of the outbreak through contact tracing and additional testing, officials said.

Johns Hopkins conducted much of the fall semester virtually, then moved to offer some in-person classes and campus housing to students this spring. University leaders have pointed to other universities that operated in-person without seeing cases of transmission in the classroom, according to the message sent to students on Wednesday.