NEW YORK - Smoking has long been known to boost tuberculosis risk, and a new study from Hong Kong suggests that being exposed to someone else's tobacco smoke also increases the likelihood of contracting the disease.

Dr. Chi C. Leung of the Wanchai Chest Clinic in Wanchai and colleagues compared TB risk in older women living with at least one smoker to that of women living in smoke-free homes. The study included 15,486 non-smoking women 65 to 74 years old, all of whom lived with their husbands. All of the women had enrolled at one of the territory's 18 Elderly Health Centers between 2000 and 2003, and about one in four lived with a smoker.

During follow-up, which lasted through the end of 2008 (or until a person died or was diagnosed with TB), 117 women developed active TB and 69 of these cases were confirmed in a laboratory.

Leung's team found that women who had been exposed to secondhand smoke were 1.5 times more likely to develop active TB than women who didn't live with a smoker, while their risk of culture-confirmed TB was 1.7-fold higher.

Secondhand smoke exposure accounted for about 14 percent of active TB cases and about 18 percent of culture-confirmed TB cases.

The researchers also found that the women who lived with a smoker were significantly more likely to have some type of obstructive lung disease, such as emphysema, as well as diabetes, at the study's outset.

The findings appear in the latest issue of the Archives of Internal Medicine.

In a written commentary published with the study, Dr. Neal L. Benowitz of the University of California San Francisco notes that secondhand smoke has many known harmful effects, including increasing the risk of lung cancer and heart disease in adults and promoting asthma and lower respiratory illness in children. And smoking can promote respiratory infections, such as TB, by impairing the ability of the lungs to fight off infection, he adds.

In China, 60 percent of men smoke, but only 4 percent of women do, Benowitz notes, so secondhand smoke disproportionately affects women.

"Secondhand smoke exposure is another health problem of particular concern for women in less developed countries," he adds. "Therefore, smoking bans should be part of the international women's health advocacy agenda."