Although still rare, drug-resistant tuberculosis (TB) is on the rise. Drug-resistant strains don't respond well-or at all-to first- and second-line TB treatments.

In the United States, 74 cases of a strain called "extensively drug-resistant TB" have been reported since 1993. Almost impossible to cure, this strain is as easily transmitted through the air as other types of TB. Another strain called "multidrug-resistant TB" was diagnosed in 128 people in the United States in 2004, which represents a 13% increase from 2003.

In the United States, the spike in drug-resistant TB is linked to infected immigrants, migrant workers, and tourists, who may not know they're ill, and to patients being treated for TB who stop taking their drugs prematurely. Treatment, which is burdensome and expensive, must continue for 2 years or more to cure some strains, if they're curable at all. Worldwide, TB kills an estimated 2 million people a year.

Source