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Outdoor Air Pollution and Tuberculosis

Posted by plosmedicine on 31 Mar 2009 at 00:05 GMT

Author: Aaron Cohen
Position: Principal Scientist
Institution: Health Effects Institute, Boston, MA
Additional Authors: Sumi Mehta
Submitted Date: February 06, 2007
Published Date: February 7, 2007
This comment was originally posted as a “Reader Response” on the publication date indicated above. All Reader Responses are now available as comments.

The meta-analysis by Lin and colleagues is important for two reasons. It evaluates the evidence concerning exposure to combustion-derived air pollution and tuberculosis (TB), and it quantifies the risk of TB associated with three important sources of exposure: tobacco smoking, ETS, and indoor burning of solid fuels. Their analysis invites speculation about the possible role of another combustion source, outdoor urban air pollution, a growing problem in developing countries where the burden of disease from TB is greatest.

Combustion-source air pollution affects resistance to infection via effects on airway resistance, epithelial permeability, and macrophage function (Thomas and Zelikoff 1999). Studies suggest a specific role for fine particles (PM2.5) (Zelikoff 2003). PM-associated transition metals, e.g. iron, are thought to produce oxidative stress in the lung, hypothesized to be a common factor in a range of adverse effects (Kelly 2003), and have been associated with altered host defenses in rats (Zelikoff 2002). As Lin notes, the amount of iron in the lung has also been hypothesized to adversely affect the progression of TB (Boelaert 2003, De Voss 1999).

Air pollution from outdoor sources, such as motor vehicles, industry, and neighborhood-level solid waste burning is associated with increased morbidity and mortality from respiratory infections in children and adults (Romieu 2002, Zanobetti A 2000). Only one study of outdoor air pollution and tuberculosis has been reported in the peer reviewed literature to date (Xu 1995), but one might speculate that outdoor air pollution would have a similar impact on TB infection and /or progression of disease via the mechanisms described above.

People in urban areas of developing countries are exposed to the highest levels of outdoor air pollution in the world, which each year impose an estimated burden of hundreds of thousands of deaths and millions of years of healthy life lost from cardiovascular disease, selected respiratory diseases, and lung cancer (Cohen AJ 2004). TB was not considered due to lack of evidence, so these estimates assume that outdoor air pollution plays no role. If, however, air pollution exposure increases the risk of infection, illness, or death from TB, then the attributable burden of disease would be even greater.

Environmental policy in developing countries should be informed by the best and most complete information on the health effects of air pollution. New research efforts should address health outcomes of regional relevance, such as TB and childhood respiratory illness. Since TB is endemic in many developing countries, even a small increase in risk could translate into a large attributable burden. Research on outdoor air pollution and TB seems warranted.

Aaron J Cohen MPH, DSc
Sumi Mehta MPH, PhD
Health Effects Institute
Boston, MA

The views expressed are those of the authors and do not necessarily reflect the views of the Health Effects Institute (HEI) or its sponsors.


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Thomas P, Zelikoff J. 1999. In: Holgate ST, Samet JM,
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Xu Z, et al. 1995. In: Air Pollution and Its Health Effects in China, ed. Chen, B. WHO. Geneva. Pp. 47-88.

Cohen AJ, et al. In: Comparative Quantification of Health Risks: Global and Regional Burden of Disease Attributable to Selected Major Risk Factors (Ezzati M, Lopez AD, Rogers A, Murray CJL, eds), vol.2. WHO, Geneva, Switzerland.

No competing interests declared.