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About 10% of mycobacterial infections are caused by nontuberculous mycobacteria. Nontuberculous mycobacterial infections are among the most common opportunistic infections in advanced HIV disease. These organisms have distinctive laboratory characteristics, occur ubiquitously in the environment, are not communicable from person to person, and are often resistant to standard antituberculous drugs.

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Henkle  E  et al. Nontuberculous mycobacteria infections in immunosuppressed hosts. Clin Chest Med. 2015;36:91.
[PubMed: 25676522]  

1. PULMONARY INFECTIONS

Mycobacterium avium complex (MAC) causes a chronic, slowly progressive pulmonary infection resembling tuberculosis in immunocompetent patients who typically have underlying pulmonary disease. Susceptibility testing for macrolide-resistance should be performed on clinical isolates. Pulmonary disease is often classified as nodular, bronchiectatic, or fibrocavitary. Treatment of pulmonary MAC requires a three-drug regimen: clarithromycin (500–1000 mg orally daily) or azithromycin (500 mg orally daily) plus either rifampin (600 mg orally daily) or rifabutin (300 mg orally daily) plus ethambutol (15 mg/kg orally daily). Therapy is continued for at least 12 months after sterilization of cultures.

M kansasii can produce clinical disease resembling tuberculosis, but the illness progresses more slowly. Most such infections occur in patients with preexisting lung disease, though 40% of patients have no known pulmonary disease. Microbiologically, M kansasii is similar to M tuberculosis and is sensitive to the same drugs except pyrazinamide, to which it is resistant. Therapy with isoniazid, ethambutol, and rifampin for 2 years (or 1 year after sputum conversion) has been successful.

Less common causes of pulmonary disease include M xenopi, M szulgai, and M malmoense. These organisms have variable sensitivities, and treatment is based on results of sensitivity tests. The rapidly growing mycobacteria, M abscessus, M chelonae, and M fortuitum, also can cause pneumonia in the occasional patient.

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Daley  CL  et al. Treatment of nontuberculous mycobacterial pulmonary disease: an official ATS/ERS/ESCMID/IDSA clinical practice guideline. Clin Infect Dis. 2020;71:905.
[PubMed: 32797222]  
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Nasiri  MJ  et al. Antibiotic therapy success rate in pulmonary Mycobacterium avium complex: a systematic review and meta-analysis. Expert Rev Anti Infect Ther. 2020;18:263.
[PubMed: 31986933]  
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van Ingen  J. Microbiological diagnosis of nontuberculous mycobacterial pulmonary disease. Clin Chest Med. 2015;36:43.
[PubMed: 25676518]  

2. LYMPHADENITIS

Most cases of lymphadenitis (scrofula) in adults are caused by M tuberculosis and can be a manifestation of disseminated disease. In children, the majority of cases are due to nontuberculous mycobacterial species, with MAC being the most common followed by M scrofulaceum in the United States and M malmoense and M haemophilum in Northern Europe. M kansasii, M bovis, M chelonae, and M fortuitum are less commonly observed. Infection with nontuberculous mycobacteria can be successfully treated by surgical excision without antituberculous therapy.

3. SKIN & SOFT TISSUE INFECTIONS

Skin and soft tissue infections such as abscesses, septic ...

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