The nontuberculous mycobacteria (NTM) are ubiquitous in the environment; so much so that some experts feel they should be referred to as “environmental mycobacteria.” Although there are more than 120 identified NTM species, the most common NTM associated with human disease are Mycobacterium avium complex (MAC), Mycobacterium kansasii, Mycobacterium fortuitum, and Mycobacterium abscessus. Many other NTM species can cause human disease but are generally rarely encountered clinically, whereas a few NTM species, most notably Mycobacterium gordonae, are frequently isolated as specimen contaminants and almost never cause disease. Infection is thought to occur from environmental exposure to the NTM with three potential portals of entry; the respiratory tract, the gastrointestinal tract, and direct inoculation of the skin and soft tissues. There are no documented occurrences of either human-to-human or animal-to-human transmission. The most common clinical manifestation of NTM infection in the immunocompetent host is chronic pulmonary disease. Symptoms are usually insidious in onset and include cough, sputum production, fatigue, weight loss, weakness, hemoptysis, and night sweats. MAC is the most common respiratory pathogen. Patients with MAC lung disease are divided between two groups. The first are primarily female patients without a history of pre-existing lung disease who have noncavitary disease characterized by nodular densities and bronchiectasis, usually in the right middle lobe and lingua. The second group are primarily male patients with pre-existing lung disease, most often chronic obstructive lung disease, and cavitary abnormalities radiographically, similar to tuberculosis.
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