Smoking could cause 18 million more cases of tuberculosis worldwide over the next 40 years and 40 million additional deaths.
That's the sobering scenario predicted by a new study led by the University of California, San Francisco (UCSF) if smoking continues at current rates.
Smoking raises the risk of contracting TB, said lead author Sanjay Basu, MD, a resident physician at UCSF. Once smokers develop the disease, they are more likely to die from it, he said. Smoking has been linked to a higher individual risk of contracting tuberculosis and to death, but until now it has been unclear how these risks could affect population-wide TB rates.
The article is published online in the BMJ (British Medical Journal).
Nearly a fifth of the world's population smokes tobacco or uses other tobacco products, a rate expected to rise in many poor countries that lack restrictions on tobacco marketing. Most of the world's smokers live in countries with a high prevalence of TB.
"The tobacco industry has spent decades working to convince developing countries as well as funding agencies that they should not 'waste' their time on tobacco control, but rather focus on infectious diseases like tuberculosis at the same time that the multinational tobacco companies were expanding aggressively in those very countries,'' Basu said. "This paper shows that, because smoking and passive smoking facilitate the spread of TB and the transition from infection to active TB, reducing tobacco use is an important key to achieving the millennium development goals for TB.''
Those goals are to cut TB mortality in half from 1980 to 2015. To achieve the target, programs of TB control have focused on detecting and treating active TB cases to reduce their infectiousness, thus breaking the transmission chain.
The senior author of the paper is Stanton A. Glantz, PhD, UCSF professor of medicine and director of the Center for Tobacco Control Research and Education at UCSF.
"Tobacco control is tuberculosis control,'' said Glantz.
For decades, UCSF has been at the forefront of research on tobacco control. The university maintains an archive of important documents including 79 million pages of formerly secret tobacco industry papers.
Until now, mathematical models of tuberculosis have taken into account the spread of HIV, the impact of new TB detection technologies and drug resistance – but not smoking. In the new study, the researchers estimated the smoking population in each of the World Health Organization's six regions to calculate the number of TB infections and deaths among smokers between 2010 and 2050, as well as the number of secondary infections and deaths resulting from each new case of TB attributable to smoking. The new model incorporates changing trends in smoking, case detection, treatment success and HIV prevalence.
The model predicted more than 18 million TB cases and 40 million TB deaths would be attributable to smoking.
"In India, for example, 38 percent of deaths from tuberculosis among middle aged men are attributed to smoking,'' the study said, "costing India's economy three times its tuberculosis budget.''
Vigorous tobacco control that results in a 1 percent drop annually in a country's smoking rates could substantially reduce the toll by 27 million deaths, the researchers said.
Sanjay Basu's research was funded in part by the Centers for Disease Control & Prevention and the National Institutes of Health.
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