e frequency of small induration sizes among TSTs was higher among smokers than nonsmokers, suggesting that smokers may be less capable than nonsmokers of eliciting a vigorous skin test reaction and that latent TB infection in smokers may thus be underdetected when the 10 mm cutoff is used. Despite this possible limitation, we found that the two studies of latent infection that used 5 mm cutoffs for the TST [32,33] reported effects that were not statistically different from those that used 10 mm [30,31,34,35]. Finally, the diagnosis of TB in children is notoriously difficult; if children exposed to passive smoke were more likely to be successfully diagnosed with disease than those who were not, this might have introduced a bias that would explain the strong positive association between passive smoking and TB.
Although our evidence suggests that tobacco smoking is only a moderate risk factor in TB, the implication for global health is critical. Because tobacco smoking has increased in developing countries where TB is prevalent, a considerable portion of global burden of TB may be attributed to tobacco smoking (see Text S1 for an illustrative calculation of population-attributable fraction and attributable deaths in different regions of the world). More importantly, this association implies that smoking cessation might provide benefits for global TB control in addition to those for chronic diseases.
Despite heterogeneity in design, measurement, and quantitative effect estimates among the studies included in this analysis, we found consistent evidence for an increased risk of TB as a result of smoking, with more limited but consistent evidence for passive smoking and IAP as risk factors. These findings suggest that TB detection might benefit from information on exposure to respirable pollutants from sources such as smoking and biomass use, and that TB control might benefit from including interventions aimed at reducing tobacco and IAP exposure, especially among those at high risk for exposure to the infection.
Text S1. Population-Attributable Fraction and Attributable Death Due to Tobacco Smoking on TB Mortality in Different Regions of the World
(33 KB DOC)
Alternative Language Abstract S1. Translation of the Article into Chinese by Hsien-Ho Lin
(64 KB PDF)
We thank Ted Cohen for providing valuable comments on the original draft and the authors of original articles (JR Glynn, K Tocque, MN Altet, R Peto, N Shetty, and M Tipayamongkholgul) of this study for helping with data collection.
HHL, ME, and MM conceived of the study and devised the search and analysis strategies. Electronic searches, expert contact, hand searches, retrieval of references were undertaken by HHL. Study selection criteria were developed by HHL and MM. Data synthesis and analysis were undertaken by HHL and MM. HHL wrote the first draft of this report and all authors contributed to the final draft.
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