Ontario public health officials are looking for 27 people who are facing a "moderate" risk of having contracted tuberculosis during a Greyhound bus trip to Windsor, Ont., on Aug. 31.

Ontario's Chief Medical Officer of Health Dr. David Williams says he doesn't want to play down the risk of infection but adds it's "not a panic situation."

The passengers don't need to be tested immediately, he said, but they should contact local public health officials as soon as possible.

A passenger on the bus had infectious tuberculosis and may have passed it on by coughing while in close contact with others.

The Greyhound excursion No. 0367 bound for Detroit left Toronto at 12:30 p.m. on Sunday, Aug. 31 with 33 passengers on board. The bus stopped in London, Ont., at 2:35 p.m. and nine more passengers got on.

The bus arrived in Windsor at 5:05 p.m. and the 27 passengers who disembarked are being urged to get tested for tuberculosis.

"Our main messaging is it's a moderate risk situation, we don't want to say it's too low because then people may ... disregard the information," Williams said.

"It's not urgent that they're going to have to rush in right away but we want them to take the notification seriously enough so they do follow up and get seen."

Most of the passengers were probably residents of Ontario, but Williams said it is possible they could be from other parts of the Canada or people returning to the U.S.

Ill passenger detained

The passenger with tuberculosis was detained at the Windsor/Detroit border by American customs officials.

The passenger had been previously diagnosed with tuberculosis and remains in quarantined care.

Williams says the passenger does not have the more serious forms of multi-drug resistant or extensively-drug-resistant tuberculosis.

The remaining 15 passengers who were still on the bus are being looked after by public health officials in the U.S. and Ontario. Williams said it's too early to know whether they were infected.

Airports routinely screen for passengers for signs of infectious diseases, but bus and train companies often don't.

A spokesman for Greyhound said it is working with Ontario public health officials and has already provided the names of the passengers on the bus.

Last May, a man previously diagnosed with extensively drug-resistant tuberculosis sparked an international stir when he ignored doctors' orders and flew from Europe to the U.S. via Canada.

Tests later showed that Andrew Speaker had the less dangerous multidrug-resistant form of TB. No one on the flight ended up infected, but some fellow passengers are suing him for putting them at risk.

Passengers who were on the bus should contact their local public health unit or phone 1-866-532-3161.