n between TB and exposure to indoor pollution from burning fuels such as wood and charcoal.
What Did the Researchers Do and Find?
In carrying out this study, the researchers wanted to base their conclusions on all the relevant information that was already available worldwide. Therefore they carried out a systematic review. A systematic review involves setting out the research question that is being asked and then developing a search strategy to find all the meaningful evidence relating to the particular question under study. For this systematic review, the researchers wanted to find all published research in the biomedical literature that looked at human participants and dealt with the association between active smoking, passive smoking, indoor air pollution and TB. Studies were included if they were published in English, Russian, or Chinese, and included enough data for the researchers to calculate a number for the increase in TB risk. The researchers initially found 1,397 research studies but then narrowed that down to 38 that fit their criteria. Then specific pieces of data were extracted from each of those studies and in some cases the researchers combined data to produce overall calculations for the increase in TB risk. Separate assessments were done for different aspects of “TB risk,” namely, TB infection, TB disease, and mortality from TB. The data showed an approximately 2-fold increase in risk of TB infection among smokers as compared with nonsmokers. The researchers found that all studies evaluating the link between smoking and TB disease or TB mortality showed an association, but they did not combine these data together because of wide potential differences between the studies. Finally, all studies looking at passive smoking found an association with TB, as did some of those examining the link with indoor air pollution.
What Do These Findings Mean?
The findings here show that smoking is associated with an increased risk of TB infection, disease, and deaths from TB. The researchers found much more data on the risks for active smoking than on passive smoking or indoor air pollution. Tobacco smoking is increasing in many countries where TB is already a problem. These results therefore suggest that it is important for health policy makers to further develop strategies for controlling tobacco use in order to reduce the impact of TB worldwide.
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.0040020.
- The World Health Organization (WHO)'s Tobacco Free Initiative provides resources on research and policy related to tobacco control, its network of initiatives, and other relevant information
- WHO also has a tuberculosis minisite
- The US National Library of Medicine's MedLinePlus provides a set of links and resources about smoking, including news, overviews, recent research, statistics, and others
- The Health Consequences of Smoking: A Report of the Surgeon General provides information on the health consequences of smoking
- Tobacco Country Profiles provides information on smoking in different countries
Tuberculosis (TB) causes an estimated 2 million deaths per year, the majority of which occur in the developing world. Many studies conducted over the past 60 years have found an association between tobacco smoking and TB, as manifested by a positive tuberculin skin test (TST) or as active disease and its sequelae. A smaller number have found that indoor air pollution from biomass fuels (IAP) and passive smoking are also risk factors for TB and its sequelae. Tobacco smoking has increased substantially in developing countries over the past three decades, with an estimated 930 million of the world's 1.1 billion smokers currently living in the low-income and middle-income countries [1,2]. Approximately half of the world's population uses coal and biomass, in the form of wood, animal dung, crop residues, and charcoal as cooking and heating fuels especially in Africa and Asia. Given the persistent or growing exposure to both smoking and IAP in regions where TB p