The student, whose identity has not been made public, attended class and commuted to school on BART from an off-campus home in Contra Costa County.
The student, who had not been vaccinated for measles, was likely infected with measles during a recent trip abroad.
"Measles is a serious, highly contagious disease," Dr. Janet Berreman, health officer for the City of Berkeley, said in a statement. "It spreads through the air, when an infected person coughs or sneezes. Fortunately, the measles vaccine is highly effective in preventing infection."
Contra Costa Health Services, the California Department of Public Health, the university and City of Berkeley Public Health are retracing the student's steps and notifying people who were in close contact with him. The agencies have identified no other measles infections related to this case, Berreman said.
The measles virus can stay in the air for long as 2 hours.
BART cars circulate throughout the Bay Area, therefore anyone who used the transit system from Tuesday, Feb. 4, to Friday, Feb. 7, during the morning commute hours and late evening was potentially exposed to measles.
Those who have been vaccinated, have had measles or were born before 1957 are unlikely to catch measles, but those who were not previously vaccinated are very likely to catch measles if exposed to the virus, health officials said.
Measles symptoms can begin one to three weeks after exposure and can include high fever, runny nose, coughing and watery red eyes. A rash develops on the face and neck two to three days after the fever begins, and spreads down the body. The rash usually lasts five or six days. An infected person is contagious for several days before and after the rash appears, Berreman said.
Anyone who shows symptoms of measles should contact their healthcare provider immediately, Berreman said.