All local Michigan State University students have been asked to self-quarantine immediately for the next two weeks to contain the “exponential growth” of COVID-19 cases, county health officials sad.

At least 342 people affiliated with the East Lansing school have tested positive for the coronavirus since Aug. 24, according to the Ingham County Health Department. In the three weeks prior, there were only 23 such cases, officials said. Cases started to rise once thousands of students returned to the area for the fall semester, officials said.

At least a third of the people who tested positive had recently attended parties or social gatherings — and at least a third of those were associated with a fraternity or sorority, the health department said.