Public health authorities in the U.S., Canada and a number of other countries are searching for people who travelled with a man infected with drug-resistant tuberculosis.

The U.S. Centers for Disease Control said the man -- an American citizen -- travelled to Paris on May 12. He then took Czech Airlines flight 0104 on May 24 from Prague to Montreal. From there, he drove into the United States.

"We have no suspicion that this patient was highly infectious (when he was travelling)," CDC Director Dr. Julie Gerberding said during a teleconference from Atlanta on Tuesday.

"In fact, the medical evidence would suggest that his potential for transmission would be on the low side," she added, "but we know it isn't zero."

The type of tuberculosis the man is believed to be infected with is called extensively drug resistant TB (XDR-TB), which is a multiple-drug resistant form of tuberculosis.

This disease can be fatal, especially in people infected with HIV, and as with other forms of TB, can be spread through the air.

The Public Health Agency of Canada is asking any passengers who were on the flight to call 1 866 225 0709.

"On airplanes they re-circulate air, and there have actually been outbreaks that have been unusually severe in terms of the number of people secondarily infected," said Dr. Neil Rau, an infectious diseases specialist in Toronto.

"So it's not just the person sitting next to the original case that's of concern. It's also the person sitting many aisles down ... Hopefully, there wasn't much bacteria that (the infected individual) was coughing up."

The CDC said the man has been hospitalized in respiratory isolation since May 25 -- and he is undergoing additional medical evaluation in Atlanta.

Gerberding said the CDC is concerned not only about the man's ability to transmit the disease, but the "seriousness of this organism and the chance that some passenger on this plane could be at serious risk for tuberculosis."

"In this case, the infected patient travelled on two trans-Atlantic air flights and, in doing so, may have exposed passengers and crew to XDR-TB," the agency said.

"A federal quarantine order has been issued and CDC is currently collaborating with U.S., state and local health departments, international ministries of health, the airline industry, and WHO (World Health Organization)."

The quarantine order is believed to be the first since 1963.

The CDC's Gerberding said the air passengers don't pose a risk to other people immediately because tuberculosis takes a long time to incubate.

Her agency isn't recommending mandatory testing of all passengers on the two aircraft.

"This would be part of a personal decision of their own health risk assessment," she said.

"But we would strongly recommend that those people seated next to the passenger and two rows behind him and two rows in front of him to be followed for a baseline skin test to make sure they weren't infected in the past and to be retested in several weeks to make sure they don't have an incubating TB infection," Gerberding said.

The man travelled to Europe on Air France Flight 385, leaving Atlanta, Ga. (where he is a resident) on May 12 and arriving in Paris on May 13.

After arriving in Montreal on May 24, it's believed he then drove to New York City, first crossing the border between Lacolle, Que., and Champlain, N.Y.

Officials with the Montreal Public Health Department said the city's residents should not be concerned about infection.

"You're only infectious with tuberculosis when you have the disease in your lungs. So having just been exposed -- or even being infected -- doesn't put you at any risk for anybody else," the department's Dr. Terry Nan Tannenbaum told CTV Montreal.

"So in this case the only concern that we might have is for passengers in Montreal who were on the flight. The person then left Montreal and the period of time that the patient spent in Montreal was just not enough to make us concerned at all."

The CDC said the man had been advised by public health authorities in Georgia that he should not travel. But it's not clear whether he knew at the time of his departure that he was carrying the XDR-TB strain.

XDR-TB is very rare in North America:

• In the U.S., there were only two cases last year and a total of 49 between 2003 and 2006.
• Canada had one case in 2003 and another in 2006.
• Tuberculosis rates in general have been falling in the U.S. The all-time low of 13,767 cases was reached last year, about 4.6 cases per 100,000 Americans.
• In Canada, there were 1,616 cases in 2005, or about five cases for every 100,000 Canadians.
• Foreign-born Canadians account for 63 per cent of the cases. Worldwide, tuberculosis kills about two million people per year.

With files from Associated Press