Association between cigarette smoking and pulmonary tuberculosis in men: A case-control study in Mazandaran, Iran

Background: The annual risk of tuberculosis (TB) in Iran is about 0.5% with annual incidence rate of 23/100000 (16322 cases). Different factors have been postulated as TB predisposing factors. Several studies have linked smoking with pulmonary tuberculosis as the TB incidence in their adult men was 2.4 times higher than women. In Iran, however, this ratio is equal and somewhere the ratio in women is greater. We decided to carry out a case control study in order to evaluate the effect of cigarette smoking on pulmonary TB. Patients and methods: A case-control study was achieved in health care centers of Mazandaran province (affiliated to Mazandaran University of Medical Sciences). Participants were men aged 15 years and older who were enrolled in health care centers with the diagnosis of active pulmonary tuberculosis. One hundred men (aged 15-85 years) with bacteriological TB (smear or culture positive) were selected as cases and 300 age-matched men without TB were selected randomly as controls. Information on smoking status, quality of tobacco smoked and duration of cigarette smoking and also the age at which smoking was first commenced were collected by a questionnaire. Results: Smokers were 2.1 times more likely to develop pulmonary TB (OR=2.10, 95% confidence interval (CI):1.33- 2.33, p < 0.04). The age adjusted odds ratio was 1.804 (95%CI:1.66-2.5, p < 0.05). Quantity of cigarette smoking and duration of smoking had positive association with pulmonary TB. The ORs for mild (1-10 cigarette/day), moderate (11- 20/day) and heavy ( > 20/day) smoking were 1.68, 2.46, and 2.56, respectively (p < 0.05). The ORs for duration of smoking with < 10 years, 11-20 years and > 20 years of smoking were 0.91, 2.48, and 2.9, respectively (p < 0.001). Conclusion: We conclude that smoking may increase the risk of pulmonary TB in men. Further studies should be conducted to investigate this association and to establish whether smoking reduction strategies contribute to tuberculosis control.