Boston, MA – Tuberculosis (TB) is an infectious disease that causes an estimated 2 million deaths each year. The majority of those deaths occur in developing countries, home to more than 900 million of the world’s 1.1 billion smokers. In addition, about half of the world’s people cook and heat their homes with coal and biomass fuels such as wood, animal dung and charcoal, which generate indoor air pollution. In a new study, researchers from the Harvard School of Public Health (HSPH) undertook a systematic review and meta-analysis of epidemiologic data to quantitatively assess the association between smoking, passive smoking and indoor air pollution and TB. They found consistent evidence that smoking is associated with an increased risk of TB; they also found that passive smoking (secondhand smoke) and the burning of biomass fuels was associated with an increased TB risk.

The study appears online on January 16, 2007, in the open-access journal PLoS Medicine.

“The evidence suggests that, when compared to non-smokers, smokers have about double the risk of tuberculosis. The implication for global health is critical,” said Megan Murray, associate professor of epidemiology at HSPH. “Since tobacco smoking has increased in developing countries where TB is prevalent, a considerable portion of the global burden of TB may be attributed to tobacco. Importantly, this also implies that smoking cessation might provide benefits for global TB control in addition to those for chronic diseases.”

The HSPH researchers, Hsienho Lin, graduate student, Majid Ezzati, associate professor of international health and Megan Murray, associate professor of epidemiology, reviewed studies from 1950 to early 2006 that explored the association between smoking, passive smoking and indoor air pollution and TB infection, disease and mortality. All the studies involved people with TB or at risk from TB. After initially identifying 1,397 papers for potential inclusion, the authors selected 38 that met their criteria for the final analysis.

The researchers found that, compared with non-smokers, smokers have an increased risk of having tuberculosis infection, of having active TB disease, and of dying from the disease. They also found evidence of an association between passive smoking and indoor air pollution and an increased risk of TB, though the evidence was more limited due to a substantially smaller number of studies. The researchers advocate larger rigorously designed studies in the future to substantiate that association.

“Our findings suggest that information on people’s exposure to respirable pollutants from sources such as smoking and biomass use will help TB detection efforts. Additionally, TB control programs may benefit from including interventions aimed at reducing tobacco and IAP exposure, especially among those at high risk for exposure to infection,” said Ezzati.

“Tobacco Smoke, Indoor Air Pollution and Tuberculosis: A Systematic Review and Meta-Analysis,” Hsienho Lin, Majid Ezzati, Megan Murray, PLoS Med 4(1): e20.

This review was supported by The International Union Against Tuberculosis and Lung Disease through a grant from the World Bank.

In a related study, Ezzati and collaborators from the Chinese Center for Disease Control and Prevention authored the first assessment of the community effectiveness of stove and behavioral interventions for reducing indoor air pollution exposure in China. This study found that ventilated heating stoves were effective in reducing indoor air pollution but there was limited benefit from alternative cooking stoves. Health behavior education alone, without increased access to alternative fuels and stoves, did not reduce indoor air pollution. The authors argue that reducing the burden of various infectious and chronic respiratory diseases for billions of people exposed to indoor smoke from cooking and heating requires investment in distributing alternative fuels.

“Community Effectiveness of Stove and Health Education Interventions for Reducing Indoor Air Pollution From Solid Fuels in Four Chinese Provinces,” Zheng Zhou, Yinlong Jin, Fan Liu, Yibin Cheng, Jiang Liu, Jiaqi Kang, Gongli He, Ning Tang, Xun Chen, Enis Baris and Majid Ezzati, Environmental Research Letters 1: 014010 (2006) http://www.iop.org/EJ/abstract/1748-9326/1/1/014010