U.S. federal health officials say they are trying to contact people who may have been exposed to drug-resistant tuberculosis after an infected U.S. man recently took two trans-Atlantic flights.

Dr. Martin Cetron of the U.S. Centers for Disease Control (CDC) told reporters Wednesday that finding the passengers who sat within two rows of the patient on those two flights is a "cumbersome and challenging and difficult process." The patient, whose name has not been officially disclosed, flew from Atlanta, Georgia, in the United States to Paris, France, on Air France flight 385 May 12. He returned on Czech Air flight 104 from Prague to Montreal, Canada, on May 24.

Cetron also said doctors believe the patient's degree of infectiousness is low. The patient is currently in isolation and under armed guard at an Atlanta health care facility.

The head of the CDC, Julie Gerberding, said the man has not broken any laws.

Officials say they did not realize his illness was the drug-resistant variety until after he had left the country. They reached the man on his honeymoon in Italy, where they warned him not to take a commercial flight back to the United States. He then flew into Canada, entered the United States by car, and checked himself into a New York hospital. Health authorities later transferred him to Atlanta.

Tuberculosis is uncommon and treatable in the United States, but is still a health threat in many other countries.

Some information for this report was provided by AFP, AP and Reuters.