Maryland health officials are warning passengers who took an Amtrak train from Boston to Virginia last week that they might have been exposed to measles from an infected passenger. Northeast Regional train #171 departed Boston last Wednesday at 8:15 a.m., with stops in New York, Philadelphia, and Washington, D.C., before reaching Lynchburg, Va., about 8:30 p.m.
Anyone who got off the train before the passenger got on in Philadelphia is not at risk, health officials said. Those who have not been vaccinated against measles should call their doctor immediately if they see symptoms within two weeks such as malaise, cough, or fever. The hallmark rash might not occur until a few days after initial symptoms.
“We believe the risk is low for passengers who boarded in Boston,’’ said Katinka Podmaniczky of the Boston Public Health Commission. “If they got off the train at or before Philadelphia, they are at no risk. In addition, most people have been vaccinated against measles and would therefore be immune.’’
Massachusetts has seen a surge in measles this year, with nearly 20 cases reported so far. In each of the previous four years, the state had just one to three cases reported. Health officials have tracked most of the cases to people who have traveled to France or other countries experiencing measles outbreaks.
While most young people in the United States have received the measles-mumps-rubella vaccine, middle-aged adults and those not up to date on their immunizations may be susceptible to the measles virus, which is extremely contagious.
Anyone riding in the same train car as an infected individual can have enough exposure to the airborne virus to be infected.
Deborah Kotz can be reached at dkotz@globe.com. 
