Surveying the association between asbestos exposure and pulmonary tuberculosis

Asbestosis, a disorder arising from fibrillar mineral compounds of hydrose silicat, damages lungs and causes respiratory signs. Asbestosis is a risk factor for pleural neoplasm, and tuberculosis has been proposed as a risk factor for progression of asbestosis and a complication in advanced asbestosis. We have surveyed the association between asbestos exposure and pulmonary tuberculosis in a group of Iranit factory workers in Tehran. During this single-blind historical cohort study, 202 asbestos- exposed workers (case group) and 201 non-exposed workers (control group) were compared regarding the clinical and paraclinical studies, including CBC,ESR, PPD, CXR, sputum and BAL fluid smear and culture for mycobacterium tuberculosis. Groups were matched according to the sex, age, duration of exposure and smoking habit.�Of the case and control groups, 7 (3.5%) and 1 (0.5%) subjects were revealed to be infected by TB, respectively. Cumulative Incidence Risk (CIR) was 6.96 showing asbestos-exposure predisposes subjects to TB. Positive PPD of more than 15 mm in case and control groups was 14.4% and 21.9%, respectively. It means that asbestos-exposure decreases reactivity to PPD. (p< 0.05) Exposure to asbestos predisposes subjects to secondary tuberculosis, possibly by reactivation of dormant foci of TB in lung. So periodic examination of exposed subjects is strongly suggested and is indicated for early detection and management.