This is the VOA Special English Health Report.

The World Health Organization recently reported that the number of cases of tuberculosis has been falling since two thousand six. Also, fewer people are dying from TB. But a study by researchers at the University of California, San Francisco, says smoking could threaten this progress.

Nearly twenty percent of all people use tobacco, and millions of non-smokers get sick from breathing the smoke. The new study predicts that smoking will produce an additional thirty-four million TB deaths by twenty-fifty.

Efforts to control the spread of tuberculosis have mainly focused on finding and treating infections. Much less effort has been made to understand the causes. Dr. Anthony Fauci is the director of the United States National Institute of Allergy and Infectious Diseases.

ANTHONY FAUCI: "Despite our control efforts, that you still have more than a million people each year, you know, dying from TB and millions and millions getting infected, we realize it's still a very important problem. So we have to do the practical thing and we have to do the fundamental research things at the same time."

Smoking does not cause tuberculosis; bacteria cause the infection. But the study says smoking affects the nervous system in a way that makes an inactive case of TB more likely to develop into an active one.

Stanton Glantz is director of the University of California's Center for Tobacco Control Research and Education and an author of the new study. He says it shows that tuberculosis cannot be controlled unless tobacco use is controlled.

STANTON GLANTZ: "It increases the number of people who will get tuberculosis by about seven percent. It increases the number of people projected to die from tuberculosis between now and twenty-fifty by about twenty-six percent."

The study is described as the first to identify a direct link between tobacco use and rates of TB infection and death. Professor Glantz says the results should guide those creating health policies and TB control efforts.

STANTON GLANTZ: "If you want to control the infectious disease of tuberculosis, you have to control the tobacco industry and the tobacco industry's efforts to increase tobacco use, particularly in developing countries where tuberculosis is a big problem."

The study predicts that the situation will only get worse if tobacco companies continue to sell more of their products in those countries. It says strong efforts to control tobacco would not only reduce deaths from smoking-related diseases like emphysema, heart disease and lung cancer. They could also prevent millions of deaths from tuberculosis.

The study appeared in BMJ, the British Medical Journal.

And that's the VOA Special English Health Report. For more news about efforts to control tobacco, go to 51voa.com. I'm Bob Doughty.

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Contributing: Vidushi Sinha