Nontuberculous mycobacteria (NTM) are resilient bacteria that grow in virtually any environment, especially those where competing microorganisms are destroyed, such as in chlorinated water. They have been discovered in soil, dust, food, water, and domestic and wild animals. Nontuberculous mycobacteria tend to infect individuals with local (e.g., damaged skin or lung) or systemic (e.g., HIV, drugs, malignancy) defects in host defence, and their incidence and prevalence have consistently increased in the last decade. Difficulty may arise in determining whether an isolated NTM from a microbiological sample is in fact a contaminant or a pathogenic organism. In this review, we discuss the important mycobacteria involved in lung disease, factors that predispose individuals to infection, and their diagnosis and treatment according to updated guidelines. English language publications in MEDLINE and references from relevant articles from January 1, 1990 to June 28, 2009 were reviewed. Keywords searched were "nontuberculous,""mycobacteria," "diagnosis," and "treatment."

While the prevalence of Mycobacterium tuberculosis continues to decline in the developed world, the same cannot be said for non-tuberculous mycobacteria (NTM). These organisms are increasing in incidence and prevalence throughout the world. This is probably because of a combination of increased exposure, improved diagnostic methods and an increase in the prevalence of risk factors that predispose individuals to infection. Considerable confusion can arise in determining in the wide range of species whether an isolated NTM is in fact a contaminant or a pathogenic organism when isolated in sputum or bronchoalveolar lavage. This confusion combined with increasing requests for advice on the treatment of disease has led to the development of guidelines to assist the clinician in diagnosing and treating infection accurately.