Tuberculosis in U.S. Hits Record Low: CDC
Improved screening of immigrants contributes to decline
"We still have about 1 percent to 2 percent of our TB cases that have significant drug resistance," LoBue said.
Eighty-six cases of drug-resistant TB were reported in the United States in 2012, the most recent year for which complete data is available. In 2013, two cases of extensively drug-resistant TB were reported nationally, the same as in 2012, the researchers said.
"We have a very strong TB control system in the United States, but there is always a potential risk because drug-resistant TB continues to be a major problem throughout the rest of the world," LoBue said.
"There is some evidence that it might be slightly increasing," he said.
Marks said it takes as long as two years to treat drug-resistant TB, compared with six months for drug-susceptible TB.
Although the United States is seeing progress against TB, the disease is epidemic elsewhere. Worldwide, 8.6 million new cases and almost 1 million deaths were reported in 2012, according to the World Health Organization.
Nationally, U.S. health officials know elimination of TB won't happen anytime soon.
Having less than one case per 1 million people would signal elimination, LoBue said. "At the current rate of decline, we wouldn't reach that level for about 100 years," he said.