Montreal Public Health says hundreds of people may have been exposed to measles between Nov. 23 and Nov. 26. during and after a recent NATO conference held in the city.

It says one of the participants, who had not been vaccinated against the disease, received a measles diagnosis after returning to their home country and would have been contagious while in Montreal.

The health agency has listed the following locations as places of exposure: 

• Palais des congrès between Nov. 23 and Nov. 25
• Humaniti Montreal Hotel from Nov. 23 to Nov. 26
• Trudeau International Airport on Nov. 26 before 5:09 p.m.
• Toronto Pearson International Airport on Nov. 26 between 4:38 p.m. and 9:18 p.m.
• Air Canada flight AC417 from Montreal to Toronto on Nov.26 — the airplane left at 3:09 p.m. and landed at 4:38 p.m.
• Air Canada flight AC890 from Toronto to Rome on Nov.26 — the airplane left at 7:18 p.m. and arrived at Rome’s Fiumicino Airport on Nov. 27 at 9:40 a.m.

Montreal Public Health says it is the first exposure to a case of contagious measles in the city since July.