Non-tuberculous mycobacterial pulmonary infection in the immunocompetent host.

Throughout much of the world, the incidence of non-tuberculous mycobacterial pulmonary infections in immunocompetent hosts is on the rise. These organisms are widespread in the natural environment; the explanation for what appears to be an increased susceptibility among human hosts is uncertain. Among more than 120 known species, the most common pathogenic isolate in the USA is Mycobacterium avium complex. The diagnosis of pulmonary disease caused by M. avium complex requires a compatible history, suggestive radiographic findings (on chest computed tomography) and microbiologic confirmation on culture of respiratory samples (sputum or direct lung sampling). Treatment options have improved with inclusion of macrolide antibiotics in a multi-drug regimen, but failure rates remain high (20-40%) even after a prolonged course of therapy. Newer, less toxic and more effective anti-mycobacterial agents are greatly needed for treatment of this increasingly common respiratory disease.