Antibiotics are being offered to all University of Otago students and staff at Studholme College after a student was diagnosed with meningococcal disease.
It's the third diagnosed case at the college this year.
The Southern District Health Board confirmed the student is doing well in Dunedin Hospital.
Medical Officer of Health Keith Reid said it was rare for two or more people to be diagnosed with meningococcal disease at a college.
"If only one student developed meningococcal disease the risk to everyone else is no different than usual," Dr Reid said.
"In this circumstance however, where two students had developed the same strain of meningococcal disease and a third is possible, the risk to others is increased."
Antibiotics were also offered to people who had close contact with the student, he said.
The disease is spread by coughing, sneezing or contact with liquids from the nose and throat.
The board confirmed the two students diagnosed in March and May have since recovered.
It said another student was treated earlier this week, but they were not linked with the college.
Symptoms of the disease include a high fever, headache, sleepiness, joint and muscle pain, a dislike of bright light and vomiting.