RESUMEN
Tuberculosis has been declared as a global emergency. Latent tuberculosis infection (LTBI) is a state in which host immunity cannot completely eradicate Mycobacterium tuberculosis. Cigarette smoke increases the risk of respiratory infections, such a TB, as it has adverse effects on respiratory immune function. In this cross-sectional study, which was performed from 2016 to 2017, 31 patients with newly diagnosed lung cancer, 63 Chronic obstructive pulmonary disease (COPD), 46 with problems in respiratory system, and 40 healthy subjects were studied. Demographic data of all subjects were recorded via a questionnaire. IGRAs (Interferon-γ release assays) were used to determine LTBI. We showed that smoking has significant odds ratio for COPD patients (OR: 4.58, 95% CI: 1.93-10.87). Also, the concordance of smoking with COPD (OR: 22, 95% CI: 2.7-179.2), lung cancer (OR: 10, 95% CI: 1.03-97), and other respiratory diseases (OR: 4.54, 95% CI: 1.93-10.87) is a significant risk factor for the presence of LTBI whereas the existence of LTBI in the study groups did not show any significant odds ratio. This study is the first to analyze the relationship between smoking in patients with respiratory diseases and LTBI susceptibility in Iran by IGRAs, which proposes cigarette smoking as a powerful risk factor for LTBI.