BERKELEY (CBS SF) — A University of California at Berkeley student with the measles rode on public transit and spent time on campus before diagnosed, Berkeley Public Health officials said Monday.

The student was diagnosed and placed into isolation on Aug. 29, but was probably contagious as early as Aug. 24, officials said.

During the infectious period before the rash appeared the student spent time on the UC campus and in the community. On Monday Aug. 24, the student took the AC Transit bus 25-A from campus at 3:30 p.m. and returned by the same bus at 5:30 p.m., officials said.

City and state health officials are working with the university to identify those living and working in close contact with the affected student.

The measles virus is highly contagious and can linger in the air for up to two hours, so residents could have been exposed in a number of places, officials said.

Symptoms develop anywhere from seven to 21 days after exposure and include fever and a facial rash.

Those at highest risk from measles are the unvaccinated, infants, pregnant women and those with impaired immunity. Those who have had the recommended two doses of the MMR vaccine are at very low risk, officials said.

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