Story highlights A Cal Berkeley student diagnosed with the measles may have exposed others

Health officials issue warning to classmates, those who commuted on BART

"Measles is a very serious viral illness, and it is very contagious," official says

Could simply sitting on a train or in a classroom land you in the hospital?

That's a possibility in Northern California, where health officials are trying to get the word out that a University of California, Berkeley, student may have exposed classmates and strangers to measles.

The school's university health services said a student who contracted measles -- likely during a trip overseas -- had spent time in and around campus and commuting to and from his home in Contra Costa County on Bay Area Rapid Transit, or BART, trains during the February 4 to 7 morning commutes and in the late evening.

In the process, he may have infected any number of people, and not just those he rubbed elbows with or shared bodily fluid with. As the Centers for Disease Control and Prevention notes , measles spreads through coughing, sneezing or breathing and "any child who is exposed to it and is not immune will probably get the disease."

Erika Jenssen, the communicable disease program director for Contra Costa Health Services, said Thursday even those who shared the same airspace as the infected student 1 to 2 hours after the fact -- and who have not been vaccinated for measles -- may get sick.

"Measles is a very serious viral illness," Jenssen told reporters, "and it is very contagious."

The good news is that the majority of Americans can't get it, because they are vaccinated for life. The Berkeley student, though, was not vaccinated.

Measles start out much like a common cold, with high fevers, red eyes and a telltale rash often following.

Children are particularly susceptible: About 10% of them who get measles come down with ear infections, and roughly 5% end up with pneumonia. One or two of 1,000 children with measles die, according to the CDC.

Measles vaccinations typically are given at an early age and over multiple rounds. A person isn't considered fully vaccinated until they have gone through the whole gamut, meaning that young people midway through that process still may be at risk.