Passive smoking linked with TB risk in children

A study conducted in South Africa suggests there is an association between passive smoking and increased risk of Mycobacterium tuberculosis infection in children living in a home with a tuberculosis patient.

"Tuberculosis and smoking are both significant public health problems," Dr. Saskia den Boon, of KNCV Tuberculosis Foundation, The Hague, Netherlands, and colleagues write in the April issue of Pediatrics. The possible association between passive smoking and TB infection in children "is a cause of great concern, considering the high prevalence of smoking and tuberculosis in most developing countries."

The team conducted a community survey that included 15 percent of the addresses in two adjacent low- to middle-income suburbs in Cape Town. All children younger than 15 years of age and their adult household members living at the addresses were included in the study.

All of the children received a tuberculin skin test, with M. tuberculosis infection defined as a reaction of at least 10 mm. The team defined passive smoking as living in a home with at least one adult who smoked for at least 1 year.

A total of 1344 children were included in the analysis. Of these, 432 (32 percent) had a positive tuberculin skin test and 1170 (87 percent) were classified as passive smokers.

The rate of positive tuberculin skin tests was 34 percent in children with a smoker in the home compared with 21 percent in those who were not passive smokers. The difference was not statistically significant.

However, there was a significant association between passive smoking and a positive tuberculin skin test in the 172 households that had with a patient with tuberculosis. Children living in these conditions were nearly five-times as likely to test positive.

"Passive smoking might affect the immune system of the child, thus increasing the risk of getting infected," den Boon and colleagues suggest. Tobacco smoke exposure alters cell function, such as lowering the rate of clearance of inhaled substances and abnormal permeability of cells and blood vessels.

The investigators note that "in many developing countries with a high burden of tuberculosis, the prevalence of smoking is rapidly increasing, especially among women." The proportion of women who smoke is particularly worrisome, they add, "because they expose their children to tobacco smoke."

SOURCE: Pediatrics, April 2007.