Smoking May Increase Tuberculosis Risk

Experts say study finding is one more reason to quit

THURSDAY, June 30, 2005 (HealthDayNews) -- If you smoke, you might be at increased risk of tuberculosis, a new study suggests.

"We found that the risk of tuberculosis infection is increased if you smoke," said lead researcher Saskia den Boon, from the Desmond Tutu TB Centre, Department of Pediatrics and Child Health at Stellenbosch University, Cape Town, South Africa.

"This is one of the first papers showing an association between smoking and risk for tuberculosis infection," added study co-author Dr. Nulda Beyers, also from Stellenbosch University.

The researchers surveyed 2,401 adults from two communities in South Africa. They asked how much each person smoked and they also administered a skin test to identify tuberculosis.

den Boon's team found that among 1,309 current and former smokers, 82 percent tested positive for tuberculosis. In addition, the researchers found that the longer one smoked, the greater the risk of tuberculosis.

The report appears in the July issue of Thorax.

"The reason for the increased risk of infection in smokers is unclear," den Boon's team wrote. They speculate that it may have something to do with the effect of smoking on the lung's ability to fight infection.

While they did not prove a causal relationship between smoking and tuberculosis, the researchers believe it is something worth investigating.

"These are two things [smoking and tuberculosis] happening in poor countries, and both are preventable," Beyers said. "Perhaps if one is more active with smoking-cessation programs, then that can help. We need to think differently, and not think only smoking and lung cancer. In poor countries, we must think smoking and tuberculosis."

Tuberculosis is a potentially fatal disease caused by bacteria called Mycobacterium tuberculosis that usually attack the lungs.

One tuberculosis expert found the study intriguing, but suggested that other factors may be at play.

"This is an interesting finding suggesting that smoking may be a risk factor for latent tuberculosis infection," said Dr. Jean Nachega, a research associate from the Johns Hopkins Center for Tuberculosis Research.

"However, one major limitation of the study is that this finding may have been confounded by HIV infection, which is known to be a major risk factor for tuberculosis in a country such as South Africa, where TB/HIV co-infection is highly prevalent," she added.

Another Johns Hopkins expert offered a different explanation for the finding.

"Smoking is often done in bars in South Africa, so it could be a marker for exposure to tuberculosis in these crowded areas," said Dr. Richard E. Chaisson, a professor of medicine and director of the Johns Hopkins University Center for Tuberculosis Research.

Nonetheless, Dr. Norman H. Edelman, chief medical officer of the American Lung Association and dean of the School of Medicine at the State University of New York at Stony Brook, said the new study was one more reason not to smoke.

"If you make a list of why smoking is bad for you, it runs three pages, and this is on the list," he said.

Another study in the same issue of the journal found that people with poor lung function have an increased risk of lung cancer.

Dr. Don Sin, of the Center for Cardiovascular and Pulmonary Research at St. Paul's Hospital, Vancouver, Canada, and colleagues looked at data from four studies that examined the relationship between lung function and lung cancer.

Among 204,990 participants in these studies, 6,185 had lung cancer or died from the disease. The researchers found that for men who had the worst lung function, the risk of developing lung cancer was more than twice that of people with the best lung function. For women, the risk was almost four times as high.

Since even small changes in lung function can signal a chance of lung cancer, Sin's group thinks its finding might be useful in screening people to detect cancer at its earliest stages, when it is most likely to be cured.

More information

The National Institute of Allergy and Infectious Diseases can tell you more about tuberculosis.

SOURCES: Saskia den Boon, Ph.D., Desmond Tutu TB Centre, Department of Pediatrics and Child Health, Stellenbosch University, Cape Town, South Africa; Nulda Beyers, M.D., director, clinical studies, Desmond Tutu TB Centre, Department of Pediatrics and Child Health, Stellenbosch University, Cape Town, South Africa; Jean Nachega, M.D., M.P.H., research associate, Johns Hopkins Center for Tuberculosis Research; Richard E. Chaisson, M.D., professor, medicine, director, Johns Hopkins University Center for Tuberculosis Research, Johns Hopkins University, Baltimore; Norman H. Edelman, M.D., vice president, Health Sciences Center, dean, School of Medicine, State University of New York at Stony Brook, and chief medical officer, American Lung Association; July 2005 Thorax
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