Spread of infection to the pleura or to extrapulmonary sites may occur in immunocompromised hosts. The newer macrolides and fluoroquinolones are active against most isolates. However, the patient's underlying disease is the most potent prognostic indicator. When isolated from immunologically intact patients, M. avium complex may be a simple contaminant or a true pathogen. M. avium complex can cause cavitary disease in patients with chronic obstructive pulmonary disease or multiple small, slowly progressing lung nodules in patients with bronchiectasis.
Most patients respond to regimens that include clarithromycin.
M. chelonei and other rapidly growing mycobacteria can also cause progressive pulmonary infections in immunocompetent hosts. Cutaneous infection can result from direct inoculation of organisms into the skin. Lesions are most common on the extremities and present as slowly enlarging papules or verrucae, which may ulcerate. The granulomas usually heal spontaneously, but this process may take months to years, and the use of surgery or chemotherapy has been advocated. M. ulcerans, which is confined to parts of Africa, Asia, Australia, and Mexico, causes a progressively destructive process called Buruli ulcer.