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A major shift in TB control strategies could be necessary following a Shanghai study that found that most cases of drug-resistant tuberculosis were caused, not by poor treatment regimes, but by patients being reinfected with a different drug-resistant strain.

The discovery counters current thinking ― that the tuberculosis (TB) bacteria mutates to become drug resistant ― and suggests that new strategies for controlling the disease are needed.

Qian Gao of Shanghai Medical School and colleagues from Shanghai Municipal Centre for Disease Control and Prevention, looked at a group of 32 patients with drug resistant TB.

To assess the level of drug susceptibility, they analysed the genetic makeup of Mycobacterium tuberculosis ― the bacteria that causes the diseasein patient samples over five years.

They discovered that in the majority of patients, samples taken at the beginning of treatment and during treatment had different genetic makeups, showing that new strains of M.tuberculosis had infected the patients, rather than an existing strain having mutated.

The results show that the assumption that poor treatment adherence usually causes drug resistance is false, Gao told SciDev.Net.

He said this might drive a major shift in strategy for controlling TB.

Multidrug-resistant TB affects over a quarter of treated TB patients in China, where some 1.3 million people are diagnosed every year.

Resistance to drugs can also build up when the initial infecting strain mutates as a result of inappropriately prescribed drugs, or patients fail to follow treatment regimes.

The study is published in the March issue of The Journal of Infectious Diseases.

Link to full paper in The Journal of Infectious Diseases

Reference: The Journal of Infectious Diseases 195, 864 (2007)

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