Silico-tuberculosis and associated risk factors in central province of Iran

Introduction: Co-existence of silicosis and tuberculosis is known as silico-tuberculosis. This article review the frequency of silicosis and tuberculosis in workers who exposed to silica and evaluate influencing factors that may increase the risk of silico-tuberculosis. Methods: An analytical cross-sectional study was performed in silica exposed workers in central province of Iran during 2011-2012. Sampling method was unrandomized and considering all workers who at least 6 months exposed to silica. The study was done via questionnaire, clinical examination, spirometry, chest x-ray and tuberculosis investigations. Results: A total of 3121 workers were included in the study, the mean age of participants was 43.1 +/- 12.4 years, and mean employment duration 14.9 +/- 6.8 years. Prevalence of TB in silica-exposed workers without silicosis was 172 cases per 100 000 people and prevalence in silicosis cases was 917 cases per 100 000 people. Incidence of TB in silica-exposed workers without silicosis was 69 cases per 100 000 people and incidence in silicosis cases was 459 cases per 100 000 people. The frequency of LTBI/TB was higher in age over thirty years old (P = 0.02), in workers with employment duration over 10 years (P = 0.004), in workers with exposure duration over 5 years (P = 0.03) and smokers with over 5 pack-years (P = 0.01). Conclusion: Exposure to silica causes a renewed multiplication of bacilli in the healing TB lesions. Prevalence of pulmonary tuberculosis in Silicosis is more common when compared to prevalence in general population, hence all should use prophylactic measures Intensification of work place.