More than 50 tourists were hospitalized for possible food poisoning Sunday night after arriving in Washington, D.C. from New York.
The D.C. health department said Monday they suspect members of the group have norovirus, which is highly contagious.
Firefighters were called to the Hotel Harrington in downtown D.C., blocks east of the White House, for a report of multiple people exhibiting symptoms of food poisoning. A large number of medics and police officers responded, temporarily blocking traffic.
Forty-eight teenagers and three adults were taken to hospitals. There were so many patients that the D.C. fire department had to use ambulance buses.
It's not clear what made the tour group sick, but fire officials said some members of the group had been sick prior to their arrival in D.C. Some members of the group had no symptoms but were hospitalized as a precaution.
Norovirus can be transmitted person to person and from contaminated food or liquids. Symptoms include diarrhea, vomiting and nausea.