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Key Features

Essentials of Diagnosis

  • Chronic cough, sputum production, and fatigue

  • Less commonly, malaise, dyspnea, fever, hemoptysis, and weight loss

  • Parenchymal opacities on chest radiograph, most often with thin-walled cavities or multiple small nodules associated with bronchiectasis

  • Isolation of nontuberculous mycobacteria in a sputum culture

General Considerations

  • Nontuberculous mycobacteria (NTM) or atypical mycobacteria are ubiquitous in water and soil

  • NTM may colonize the airways or appear in cultures due to environmental contamination

  • Organisms are not communicable from person to person

  • NTM are often resistant to most antituberculous drugs

  • Complementary data are important for diagnosis, as NTM can reside or colonize airways without causing clinical disease

  • Mycobacterium avium complex (MAC) is the most common cause of NTM pulmonary disease in the United States

  • Mycobacterium kansasii is the second most common pulmonary pathogen

  • Other NTM that can cause pulmonary disease include

    • Mycobacterium abscessus

    • Mycobacterium xenopi

    • Mycobacterium malmoense

  • Most organisms cause a chronic progressive pulmonary infection similar to tuberculosis but more slowly progressive

  • Many patients have AIDS or preexisting lung disease

  • Disseminated disease is rare in immunocompetent patients

  • Disseminated MAC infection is common in patients with AIDS

Clinical Findings

Symptoms and Signs

  • Chronic cough, sputum production, and fatigue

  • Malaise, dyspnea, fever, hemoptysis, and weight loss are less common

  • Symptoms from coexisting lung disease can confound the evaluation

  • New or worsening infiltrates, adenopathy, or pleural effusion are described in HIV-positive patients with NTM infection as part of the immune reconstitution inflammatory syndrome following institution of antiretroviral therapy

Differential Diagnosis

  • Postviral

  • Bronchitis, especially in smokers

  • Bronchiectasis

  • Tuberculosis

  • Cystic fibrosis

  • Pertussis

  • Mycoplasma

  • Chlamydia

  • Respiratory syncytial virus

Diagnosis

Laboratory Tests

  • Diagnosis rests on recovery of the pathogen from cultures

  • Bronchial washings are considered more sensitive than expectorated sputum, but their specificity for clinical disease is unknown

  • Bacteriologic diagnostic criteria in immunocompetent persons include

    • Positive culture results from at least two separate expectorated sputum samples; or

    • Positive culture from at least one bronchial wash; or

    • Positive culture from pleural fluid or any other normally sterile site

  • Criteria for infection in HIV-positive patients is less stringent

  • DNA probes or high-pressure liquid chromatography allow rapid species identification of NTM

  • Drug susceptibility testing is recommended only as follows:

    • M kansasii and rifampin

    • Rapid growers (Mycobacterium fortuitum, M abscessus, and M chelonae) and amikacin, doxycycline, imipenem, fluoroquinolones, clarithromycin, cefoxitin, and sulfonamides

Imaging Studies

  • Chest radiograph with progressive or persistent opacities for 2 months, cavitary lesions, and multiple nodular densities

  • Cavities are usually thin walled and with less surrounding opacity than seen in M tuberculosis

  • High-resolution CT scan may show multiple small nodules with or without multiple foci of bronchiectasis

  • Opacities ...

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