The research, which followed 546 college students from freshman to senior year, found the only factor that increased the risk for catching mono was deep kissing.

Students who reported deep kissing, regardless of whether or not the kissing was tied to sex, were more likely to develop mono than those who did not kiss or have sex, the researchers said.

Other factors, including the student's diet and amount of exercise and stress, failed to increase the risk, the researchers said.

Caused by the Epstein–Barr virus, mononucleosis (mono for short) is spread through contact with an infected person's saliva. It can also be spread through coughing, sneezing or sharing food, but the disease is not as infectious as a cold virus, according to the Mayo Clinic.

Many people are exposed to the virus before they reach adulthood and develop immunity to it. Symptoms include sore throat, fatigue, headache, fever decreased appetite, and swollen tonsils. However, some people develop mono without showing symptoms.

Before the study began, the researchers tested all the students' blood for antibodies against the Epstein–Barr virus. About 63 percent of the students tested positive for the antibodies, meaning they'd had mono in the past. The remainder, 143 students, visited the university clinic every 8 weeks for an average of three years,  to test if they had developed the illness.

During this time, doctors diagnosed 66 of the students with mono. Of these, 59 showed symptoms. Previously, it had not been clear how often people in this age group developed symptoms when they got mono.

Students with mono were sick for an average of 17 days, but were capable of spreading the virus for much longer — about 5 months.

The rate of infection was higher during freshman year (26 cases per 100 people) compared to the other three years (10 cases per 100 people per year).

The study, conducted by researchers at the University of Minnesota Medical School in Minneapolis, was published online Oct. 24 in the Journal of Infectious Diseases.

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