'Virtually untreatable' TB found
Extreme drug resistant TB (XDR TB) has been seen worldwide, including in the US, Eastern Europe and Africa, although Western Europe has had no cases.Dr Paul Nunn, from the WHO, said a failure to correctly implement treatment strategies was to blame.TB experts have convened in Johannesburg, South Africa, to discuss how to address the problem.TB presently causes about 1.7 million deaths a year worldwide, but researchers are worried about the emergence of strains that are resistant to drugs.Drug resistance is caused by poor TB control, through taking the wrong types of drugs for the incorrect duration.
Multi-drug resistant TB (MDR TB), which describes strains of TB that are resistant to at least two of the main first-line TB drugs, is already a growing concern.Globally, the WHO estimates there are about 425,000 cases of MDR TB a year, mostly occurring in the former Soviet Union, China and India.Treatment requires the use of second-line drugs, which are more toxic, take longer to work and costly.But now, according to researchers, an even more deadly form of the bacteria has emerged.
High prevalence
XDR TB is defined as strains that are not only resistant to the front-line drugs, but also three or more of the six classes of second-line drugs.This, according to Dr Paul Nunn, coordinator of the WHO team at the Stop TB department, makes it virtually untreatable. A recent survey of 18,000 TB samples by the US-based Centers for Disease Control and the WHO between November 2004 and November 2005 found 20% of them were multi-drug resistant and a further 2% were extreme drug resistant. Further detailed analysis of several countries found the prevalence was even higher.
In the US, 4% of all MDR TB cases met the criteria for XDR TB; in South Korea, the figure was 15%. In Latvia, and according to Dr Nunn other areas of the Balkans and the former Soviet Union, 19% of all multi-drug resistant cases were extreme drug resistant too. Dr Nunn said XDR TB was present across several strains, but added it was not yet clear how transmissible it was or whether it was limited to isolated pockets.
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