Silica, silicosis and tuberculosis

Abstract

Exposure to crystalline silica dust causes multiple diseases, but silicosis and silica dust-associated tuberculosis (TB), in particular, are the two diseases that remain high on the list of occupational health priorities in low-income countries and that still occur in some high-income countries. The prevalence of silica-related TB is exacerbated by the human immunodeficiency virus (HIV) epidemic in low-income countries. This review describes the morphology of silica and the variable potency of the different forms. Sources of crystalline silica are discussed, with emphasis on less commonly recognised sources, such as small-scale mining operations and agriculture. Trends in the prevalence of silicosis are also presented. Although efforts have been made for many years in most countries to reduce silica dust levels, silicosis continues to occur even in young people. The clinical and pathological features and diagnosis of silicosis, with emphasis on chest radiography, are described. The high risk of mycobacterial infection in silica-exposed individuals is given particular attention, with emphasis on control. Treatment for latent TB is recommended. The management of silicosis and silica-associated TB, including monitoring for early detection of disease and surveillance to identify disease-causing workplaces, are discussed in detail. Prevention of disease, in the form of dust control, remains the focus of the World Health Organization and International Labour Office Global Elimination of Silicosis Campaign. However, clinicians must be aware that silica-associated diseases will be around for many years to come.