The bacterium that causes tuberculosis grows extremely slowly. As a result, TB patients need to take antibiotics for many months in order to kill all of the bacteria. But many patients fail to complete their courses of therapy, and that has given the TB bacteria an opportunity to evolve into more virulent forms. This 'multi-drug resistant', or MDR-TB is harder to treat, and is already resistant to isoniazid and rifampicin -- the two most common drugs used to treat the disease.

Dr. Sushil Jain from the Hinduja National Hospital in Mumbai, India, says that for several years, he's seen forms of MDR-TB that are even more resistant to treatment. "It's really difficult to treat these types of patients," Jain says. "We have very few drugs left to treat these patients, and the mortality is further increased on treating these patients."

Last year, the World Health Organization identified these bacteria as 'extremely drug resistant' or XDR-TB, and its prevalence is increasing worldwide.

Jain looked at all suspected tuberculosis samples sent to the Hinduja hospital lab over one year and found that about a third of the cultures were positive for multi-drug resistant TB. Furthermore, he found that about 9 percent of those MDR samples were actually XDR-TB.

"XDR-TB was more common among [the] younger age group, with a mean age of about 30 years," Jain reports, pointing out that people in this age group make up a large portion of the economically productive population. "If these patients suffer from this form of the disease," he adds, "then it is not good for the community."

Jain says what's especially worrisome is that XDR-TB is more deadly than both normal TB and MDR-TB. "At the end of one year, about 40 percent of the patients [had] expired. So this is the inference, that the mortality of [this] group of patients is high." The percentage is lower than in a previous study, done in Africa, but Jain points to a significant difference. "In that study, it was mainly in an HIV-positive population, while our study is in the general population."

Jain's study is the first from India to compile data and estimate the prevalence of this strain of bacterium. He says more research must be done to better assess the extent of XDR-TB in India. He presented his research at the American Thoracic Society International Conference in San Francisco last week.