(Recasts with CDC, hospital officials)

By Will Dunham

WASHINGTON, June 1 (Reuters) - Authorities have contacted more than 100 people who flew on airliners with a U.S. man with a hard-to-treat type of tuberculosis but his doctors said on Friday that new exams showed it was extremely unlikely he spread the disease.

"It is our opinion that he is of low communicability," Dr. Gwen Huitt, who is treating 31-year-old Atlanta lawyer Andrew Speaker at a Denver hospital, told a news conference.

She said new chest X-rays and other tests were reassuring, he still had no cough or fever and he even rode a stationary bike.

"I think everyone should likely be able to breathe a sigh of relief, quite honestly," Huitt said.

Speaker triggered an international health alert and raised questions about U.S. border security by defying U.S. health officials, flying to and from Europe for his wedding and honeymoon, then driving freely through a U.S. border checkpoint in upstate New York while on a watch list for detention.

Speaker apologized to fellow passengers.

"I'm very sorry for any grief or pain that I have caused anyone," he told the ABC program "Good Morning America" in an interview aired on Friday from National Jewish Medical and Research Center in Denver, where he is being treated.

"I just hope they can forgive me and understand that I really believed that I wasn't putting people at risk."

Dr. Julie Gerberding, director of the U.S. Centers for Disease Control and Prevention, said U.S. authorities had contacted 74 Americans who flew with Speaker aboard an Air France flight from Atlanta to Paris to urge them to get tested for TB.

This included all 26 Americans considered most at risk because they sat within two rows of him, she said.

There were about 435 passengers on that plane, including 310 Americans, Gerberding said, adding that authorities in other countries were responsible for reaching their citizens who were on the plane.

Gerberding said Canadian authorities had reached all 28 passengers seated within two rows of Speaker on his Czech Air flight back from Europe that went from Prague to Montreal.

Gerberding said it was expected that initial skin tests would come up negative for these passengers because of the slow growth of the TB bacteria, saying they should be tested again in several weeks to really see if they have been infected.

DANGEROUS TB STRAIN

Speaker is being held under a federal isolation order for treatment for extensively drug-resistant tuberculosis, or XDR TB. While no more contagious than other TB strains, most antibiotics do not work against it. TB is a sometimes fatal bacterial infection usually attacking the lungs.

Huitt said Speaker began receiving medication on Friday and could get at least five different drugs. She said it would take four to six weeks to judge whether the treatment was working, and said surgery remained an option. Huitt said his lung infection mass was about the size of a tennis ball.

Speaker flew from Atlanta to Paris, on to Greece for his wedding and to Rome for his honeymoon.

After U.S. health authorities reached him in Rome and told him not to fly home on a commercial airliner, Speaker and his wife fled to Prague for a commercial flight to Montreal and re-entered the United States by car. He drove through a border crossing from Canada despite his name being on a list to detain due to medical reasons.

U.S. Customs and Border Protection Deputy Commissioner Jayson Ahern said the agency was investigating why an officer at the crossing failed to stop him. Ahern said agency procedures would be reviewed.

"Just because we had a breakdown by an individual doesn't mean that we need to completely throw the system out. I think we need to continue to build redundancies, continue to look at gaps and continue to go ahead and refine our protocols," Ahern said.

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