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But more than 11 million Americans have latent TB, meaning they are infected with the TB bacteria but have not had symptoms and are not infectious.
About 5 percent to 10 percent of people with latent TB develop the disease if not treated, meaning they are a major obstacle to eliminating TB in the United States.
"The 11 million persons with latent TB represent a ticking bomb. They're the source of future TB cases," said Dr. Kenneth Castro, director of the CDC's Division of Tuberculosis Elimination.
Most Americans with latent TB don't know they are infected, but testing has been targeted at groups of people who tend to have higher rates of TB infection or who are more susceptible to TB infection progressing into illness. About 300,000 to 400,000 Americans with latent TB start treatment each year.
But many don't stick with it, sometimes because they feel well and don't see the need to keep taking a pill against an illness they haven't developed. Some don't like that they cannot drink alcohol while taking isoniazid.
The study looked at about 8,000 people with latent TB in the United States, Canada, Brazil and Spain. They were followed for nearly three years from the time they started the study. Most of the top TB research centers in the United States were involved.
About half were given the standard treatment, a daily 300 milligrams dose of isoniazid for nine months, and they took it on their own. The other half were put on a 900-milligram dose of isoniazid and a 900 milligram dose of rifapentine, but did it in front of a doctor or other health-care worker.
The researchers acknowledged that follow-up studies are needed to see if patients on the three-month regimen are as faithful at taking their medicine when they aren't being monitored.
Also, it's not clear how well the strategy would work in countries where TB is more common and the odds of re-infection are much higher, health officials said.
Copyright 2011 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.
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