New York officials said Saturday that a college student who had tested positive for measles was contagious when he boarded an Amtrak train last Sunday and potentially exposed thousands of travelers to the infection, ABC News reported.

On Jan. 25, the Bard College student boarded the No. 283 train out of New York City’s Penn Station, one of the country’s busiest transportation hubs, en route to Albany and got off at the station in Rhinecliff, N.Y.

The Department of Health has advised individuals who may have been exposed or have symptoms consistent with measles to contact their doctor or local emergency room before seeking medical care in order to prevent further contagion at the facilities.

The warnings come amid a nationwide resurgence of measles linked to Disneyland theme park in Southern California. About 100 cases of the disease have been reported in the U.S. since last month, the second-largest outbreak in at least 15 years, the Associated Press reported.

The DOH has recorded three cases in New York this year.

Measles is a highly infectious disease that is spread by contact with nasal or throat secretions of infected people. Nine out of 10 unvaccinated people exposed to the measles virus will get the measles.

Symptoms include high fever, runny nose and cough, and can take as many as 18 days after exposure to appear.

The Centers for Disease Control and Prevention says measles-mumps-rubella vaccine is 97 percent effective at preventing measles. The White House has also advised parents to vaccinate their children.