Niagara Public Health is warning people to watch for signs after a confirmed case of measles.
An adult caught the infection while travelling outside of Canada.
That person was at West Lincoln Memorial Hospital in both the emergency room and X-Ray unit on February 27th.
Another exposure location was on a flight that came through Pearson Airport.
Doctor Andrea Feller, the associate medical officer of health in Niagara, says there's no need to panic.
She says it's important for people to be aware that if they haven't been vaccinated they should check for symptons for 21-30 days after the exposure.
They include a cough, runny nose watery eyes and fever. After four days, a rash begins on the face and moves down the body.
There may be white spots inside the mouth.
The airline exposure occurred on February 22 on the following flights: