Ontario health officials are searching for 27 people who may have been exposed to tuberculosis while travelling on a Greyhound bus from Toronto to Windsor on Aug. 31.

There's a "moderate risk" they contracted the disease, public health officials said Thursday.

A passenger on the bus was sick with the tuberculosis and may have spread it by coughing while in close proximity to the other bus passengers. The passenger, identified only as a woman with a Canadian passport, was detained by American custom officials at the border between Windsor and Detroit.

Ontario's Chief Medical Officer of Health Dr. David Williams said that since the woman's symptoms aren't serious, passengers shouldn't panic.

"The risk to the public is not a high one but we need to go the extra mile and make sure to contact those people the best we can," he said.

Williams said that it's not clear where the woman was sitting or which passengers face the greatest risk of infection.

The bus departed Toronto at 12:30 p.m. Sunday, and by the time it reached the U.S. border just after 5:00 p.m., 42 passengers were on board.

Health officials want to get hold of the 27 passengers who got off the bus in Windsor so they can be tested for tuberculosis.

The remaining 15 passengers have been identified and are being monitored by health officials in the U.S. and Ontario.

A representative from Greyhound told The Canadian Press that the bus company is fully cooperating and that they have provided officials with a passenger list.

Passengers who were on the bus should call their local public health department or call 1-866-532-3161.

With files from The Canadian Press