PHOENIX — Behind the county hospital’s tall cinderblock walls, a 27-year-old tuberculosis patient sits in a jail cell equipped with a ventilation system that keeps germs from escaping.

Robert Daniels has been locked up indefinitely, perhaps for the rest of his life, since last July. But he has not been charged with a crime. Instead, he suffers from an extensively drug-resistant strain of tuberculosis, or XDR-TB. It is considered virtually untreatable.

County health authorities obtained a court order to lock him up as a danger to the public because he failed to take precautions to avoid infecting others. Specifically, he said he did not heed doctors’ instructions to wear a mask in public.

“I’m being treated worse than an inmate,” Mr. Daniels said in a telephone interview with the Associated Press last month. “I’m all alone. Four walls. Even the door to my room has been locked. I haven’t seen my reflection in months.”

Though Mr. Daniels’s confinement is extremely rare, health experts say it is a situation that U.S. public health officials may have to confront more and more because of the spread of drug-resistant TB and the emergence of diseases such as SARS and avian flu in this increasingly interconnected world.

“Even though the rate of TB in the U.S. is at the lowest ever this last year, we live in a globalized world where, if anything emerges anywhere, it could come to our country right away,” said Mark Harrington, executive director of the Treatment Action Group.

The World Health Organization warned last year of the emergence of extensively drug-resistant TB. The new strain, which has been found throughout the world, including pockets of the former Soviet Union and Asia, is resistant not only to the first line of TB drugs but to some second-line antibiotics as well. How to deal with people infected with the new strain is a matter of debate.

Dr. Ross Upshur, director of the Joint Center for Bioethics at the University of Toronto, said authorities should detain people with drug-resistant tuberculosis if they are uncooperative.

“We’re on the verge of taking what was a curable disease, one of the best known diseases in human endeavors, and making it incurable,” Dr. Upshur said. But a paper Mr. Upshur co-wrote on the issue in a medical journal earlier this year has been strongly criticized.

“Involuntary detention should really be your last resort,” Mr. Harrington said. “There’s a danger that we’ll end up blaming the victim.”

In America, which had a total of 13,767 reported cases of tuberculosis in 2006, public-health authorities only rarely have put TB patients under lock and key.

Texas has placed 17 tuberculosis patients into an involuntary quarantine facility this year in San Antonio. Public-health authorities in California said they have no TB patients in custody this year, though four were detained there last year.