 This is the VOA Special English Health Report. The World Health Organization says the number of cases of tuberculosis has been falling since 2006. 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 20% of all people use tobacco. The smoke also sickenes millions of non-smokers. The new study predicts that smoking will produce an additional 34 million TB deaths by 2050. 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 director of the National Institute of Allergy and Infectious Diseases. He says more than a million people each year die from TB and millions more get infected. 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. 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. Study co-author Stanton Glantz is director of the University of California's Center for Tobacco Control Research and Education. He says tobacco use could increase the number of people expected to die from tuberculosis between now and 2050 by about 26%. 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. 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. Those efforts would also prevent millions of deaths from tuberculosis. The study appeared in BMJ, the British Medical Journal. For VOA Special English, I'm Alex Villarreal.