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Drug-resistant TB at record levels worldwide, the WHO says

March 18, 2010 |  3:23 pm

An estimated 440,000 people had multi-drug resistant tuberculosis in 2008 and a third of them died as the new variant of the TB mycobacterium continues to spread, the World Health Organization said Thursday. Nearly half of the cases were in China and India, which have been hit hardest by the outbreak. But in some areas of the world, especially three provinces in Russia, more than one in every four cases of tuberculosis are  the result of the hard-to-treat strain, according to the report.

Worldwide, there were an estimated 9.4 million cases of TB and 1.8 million deaths, so the drug-resistant forms remain a relatively small problem. But experts fear that they will continue to spread, displacing the drug-susceptible strains and greatly complicating treatment and increasing its cost.

Multidrug-resistant TB (MDR-TB) is caused by bacteria that are resistant to at least isoniazid and rifampicin, the anti-TB drugs most commonly used. It may be caused by infection with the resistant bacterium or the resistance may appear during treatment. It is most commonly caused by failure to complete the normal six-month course of treatment or the use of substandard or counterfeit drugs.  A course of treatment for MDR-TB can take as long as two years and cost as much as $500, compared with six months and $20 for treatment with standard drugs. About 60% of those who are diagnosed with the variant are cured, according to the WHO.

The numbers for MDR-TB are estimates because so many of the cases remain undiagnosed. In Africa, for example, where an estimated 69,000 cases emerged in 2008, the vast majority of them were undiagnosed. Diagnosing an MDR infection can take as long as four months using conventional tests. New, rapid tests that work in as little as two days are becoming available, but are not yet widely used, in part because the testing infrastructure is not widely available, the WHO said. That is a special problem in Africa. Only about 7% of all MDR-TB patients worldwide are diagnosed

A potentially more serious problem is extensively drug-resistant TB or XDR-TB, in which the bacteria are resistant not only to isoniazid and rifampicin, but also to a fluoroquinolone and any of the second-line injectable drugs, such as amikacin, kanamycin and capreomycin. Treatment is far more expensive than treatment of MDR-TB. No good numbers are available for the incidence of XDR-TB, but the WHO estimates there were about 25,000 cases in 2008 and that nearly all its victims died. Since XDR-TB was first reported in 2006, 58 countries have reported at least one case.

-- Thomas H. Maugh II

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