arrived in the United States, is not likely to have been highly infectious, but they had to act because of his behavior.
He has a difficult-to-treat form of TB called extensive drug resistant TB, or XDR TB.
"We believe that his degree of infectiousness is quite low," Dr Martin Cetron, director of the CDC's Division of Global Migration and Quarantine, told a news conference.
But just in case, the CDC, the World Health Organization and national health authorities in Europe are looking for 70 to 80 people who sat near him on long, trans-Atlantic flights.
The man, now being held under isolation in a hospital near his home in Atlanta, had been told by state health officials he had a drug-resistant form of tuberculosis.
"They clearly told him not to travel," Cetron said.
"In this instance, the reason for use of a federal isolation order is because of the nature of international travel and the potential for interstate spread," he added.
"We don't take this authority lightly."
The CDC has been evaluating its quarantine powers amid recent fears of a pandemic of influenza. The H5N1 strain of avian influenza has killed 186 people out of 307 infected, and experts believe it could change into a form that transmits easily from one person to another, sparking a pandemic.
Experts repeatedly point out that anyone could carry any virus around the world on a single flight.
"Anyone who's sick shouldn't be getting on an aircraft. And that is a basic principle for any contagious disease," Dr Ken Castro, CDC's director of tuberculosis elimination, told the news conference.
Cetron said, "In many ways we balance individual freedoms and the public good and we depend on a covenant of public trust."
The patient told the Atlanta Journal-Constitution newspaper that he had been in Italy on his honeymoon. He knew he had multi-drug resistant TB but traveled anyway.
When authorities told him he had XDR TB, which is much harder to treat, they also told him he would be banned from flying. He told the newspaper that he and his new wife decided to flee, flying from Italy to Prague, and from there to Montreal, where they drove across the border from Canada to New York.
The man, who began his trip by flying from Atlanta to Paris and then to Greece, told the newspaper he did not want to put anyone at risk but wanted to get home for treatment.