Tuesday, September 14, 2004

One-Third of World Population Infected With Tuberculosis

1/3 Of Global Population Infected With TB
By Shaoni Bhattacharya

The major World Health Organization programme to curb tuberculosis globally is failing to bring the disease under control, warns a new review.
The WHO's strategy to combat the widespread infectious disease involves stopping the spread of TB by treating people who have tested positive for it. Because patients can fail to follow the long courses of treatment needed for TB, WHO launched its "directly observed therapy, short course" (DOTS) where patients receive treatment under supervision.
This means they are more likely to complete treatment, which prevents further spread of the disease, as well as the development of antibiotic resistance.
But global TB rates continue to rise ñ and even soar in countries riven with HIV/AIDS ñ warn Timothy Brewer and Jody Heymann of Harvard University in Massachusetts, US. "After almost 10 years of a control strategy that has done little to reduce or to eliminate TB, global TB control needs to be reassessed," they say.
DOTS was launched after WHO declared TB a global emergency in 1993. At that time, one third of the world's population was believed to be infected by the bug ñ although many people do not show symptoms. And 7.5 million new cases and 2.5 million deaths were caused by TB every year.
But Chris Dye, co-ordinator of the tuberculosis monitoring and evaluation team at the WHO, stresses that DOTS has produced drastic cuts in TB rates in some regions. "In a very real sense DOTS is working. What these authors are saying, and we are agreeing, is that it's not working fast enough."
Latent TB
He says the paper does not acknowledge the improvements seen with DOTS. "The bottom line is although DOTS has its defects, it has to remain the foundation of TB control," he told New Scientist.
"The point of the commentary is not to say 'we think DOTS is bad' but we need to think about TB control in general ways," Brewer told New Scientist. He points out that HIV has been a "tremendous factor" in TB control over the last decade, as HIV patients are more susceptible to TB, and that control strategies need to address this.
Dye says more than 10 million people worldwide have been successfully treated over the last 10 years using DOTS. And in a recent paper in The Lancet, DOTS was shown to cut TB prevalence by a third in half of China ñ 500 million people ñ over a decade.
But the situation is complicated because many people infected with Mycobacterium tuberculosis do not develop the disease ñ two billion people globally have "latent" TB. And over half the people with TB do not test positive for the disease using a sputum smear test.
The DOTS strategy relies upon identifying TB patients using this test, and actively treating them. By concentrating on these smear positive patients, DOTS and its sister strategy for drug-resistant TB, called DOTS-Plus, are likely to have "only a modest impact" on global TB control, say Brewer and Heymann. An estimated 9.1 million people with TB worldwide test negative, note the pair, and they may be responsible for 1.4 million new infections every year.
Large backlog
Brewer and Heymann also point out that the WHO strategy is based on preventing people with the disease from spreading it, rather than overall prevention. "The lack of historical precedents for this approach is worrisome for the successful control and ultimate elimination of TB with this strategy," they write.
They suggest treating people with latent TB with an antibiotic, called isoniazid, as one strategy. However, Dye points out that this recommendation is "theoretical, not practical" as it would involve persuading people with no symptoms to take the antibiotic every day for nine months. And with a third of the world infected there would be a "very large backlog" to tackle.
But this could be attempted in the case of patients with both HIV and latent TB, who are extremely vulnerable, he says.
Dye is realistic: "Nobody is thinking about eradication at the moment ñ that won't happen for another century. What will happen is that TB is locally eliminated as a public health problem."

Journal reference: Journal of Epidemiology and Community Health (DOI: 10.1136/jech.2003.008664)

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