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Essentials of Diagnosis
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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
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General Considerations
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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
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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
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Differential Diagnosis
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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
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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 ...