The number of mumps cases at Indiana University’s Bloomington campus has more than doubled in the past week. There are now 16 cases associated with the outbreak, an increase of nine since last week.

The IU Health Center sees three to four students a day who want to be tested for mumps because they’re exhibiting symptoms.

IU Spokesperson Chuck Carney says many of the students with the virus are linked.

“Of these 16 confirmed cases we know that nine are definitely associated with one fraternity house,” Carney says. “So we feel like it is fairly well contained. It is on campus, but it is not all the way across campus at this point.”

Just over half of the members of that fraternity opted to get a third MMR vaccine dosage.

Carney says IU is advising students with mumps symptoms to get tested and isolate themselves from others. But more cases are likely.

“I believe that the period for the outbreak with these latest cases now will extend into June and the infectious period is going to go into May at this point,” Carney says.

Carney says those periods will be longer if additional cases pop up.

The university saw just five mumps cases in 2016.