In an article in the recent issue of the journal Thorax, researchers have emphasized the association between TB and smoking.
Researchers have looked into the data provided by 2401 subjects who had smoked to establish a firm connection between smoking and incidence of tuberculosis disease. Of the total subjects about 76% of them tested positive for tuberculin skin test. The research results have showed that the increase of the risk of acquiring Mycobacterium tuberculosis infection is higher in those people who had smoked for more than 15 pack-years.
A pack-year is smoking for one year at a cigarette pack a day. Smokers smoking for 30 pack-years may be all those who have smoked a pack a day for 30 years, or two pack a day for fifteen years, or three packs a day for ten years.
To have smoking as a factor for risk of tuberculosis, smoking has to generate the environment that may allow the tubercle bacilli to survive and infect one host from another. The researchers have found that this do happen in people who have been smoking for long.
Reference: Thorax, July 2005