Smoking Linked to Increased TB Risk

BOSTON, Jan. 16 -- Smokers run a higher risk than non-smokers of having latent or active tuberculosis and of dying from the disease, according to researchers here.

A systematic review of published data also shows that passive smoking and exposure to indoor pollution from burning organic substances is linked as well to a higher risk of TB, found Megan Murray, M.D., D.P.H., of the Harvard School of Public Health.

"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 (indoor air pollution) as risk factors," Dr. Murray and colleagues reported online in the Jan. 16 issue of PLoS Medicine.

The researchers found 38 studies between 1950 and 2006 that included enough data for them to calculate a number for the increase in TB risk associated with smoke, passive smoking, or pollution from the burning of fuels such as wood and charcoal.

"The evidence suggests that, when compared to non-smokers, smokers have about double the risk of tuberculosis," Dr. Murray said, adding that "the implication for global health is critical."

Because smoking is increasing in areas where TB is also on the rise, she said, "a considerable portion of the global burden of TB may be attributed to tobacco."

The implication, Dr. Murray said, is that "smoking cessation might provide benefits for global TB control in addition to those for chronic diseases."

The analysis found 33 papers on tobacco smoking and TB, five papers on passive smoking and TB, and five on indoor air pollution and TB, the researchers said.

Of the 33 papers focused on smoking, 23 looked at active TB, six at latent TB, and six looked at TB mortality. Some studies included more than one category, Dr. Murray and colleagues found.

A pooled odds ratio for the studies that focused on smoking and latent TB showed about a doubling of risk, depending on the size of the induration used to determine positivity of the tuberculin skin test, the researchers found.

The studies focusing on smoking and active TB were too variable to allow pooled odds ratios but the size of the effect was similar in most of the studies, Dr. Murray and colleagues said.

"There was a significantly increased risk of clinical TB among smokers regardless of outcome definition (pulmonary TB versus any TB), adjustment for alcohol intake or socioeconomic status, type of study, or choice of controls," the researchers said.

The evidence for the effects of passive smoking and indoor air pollution was less strong, Dr. Murray and colleagues said, perhaps because there were fewer studies looking at those issues.

An estimated two million people a year die of TB, most of them in the developing world, the researchers noted.