Microbiology

NTM are broadly differentiated into rapidly and slowly growing forms (<7 days and ≥7 days, respectively). M. abscessus, M. fortuitum, and M. chelonae are examples of rapid growers; species such as M. avium and M. intracellulare (the M. avium complex, or MAC), M. kansasii, M. ulcerans, and M. marinum are slow growers.

Epidemiology

Most NTM cause disease in humans only rarely unless some aspect of host defense is impaired (as in bronchiectasis) or breached (as by inoculation-e.g., during liposuction or trauma). The bulk of NTM disease in North America is due to M. kansasii, MAC organisms, and M. abscessus.

Clinical Manifestations

Although there are many NTM species, the clinical presentations they cause can be broadly categorized by the organ system(s) affected.

• Disseminated disease is now quite rare; even pts with advanced HIV infection do not often develop disseminated NTM infection, given improved treatment of HIV infection and effective antimycobacterial prophylaxis.
  • Organisms typically spread from the bowel to the bone marrow and bloodstream, but disease is indolent, and it can take weeks or months for the pt to present for medical attention with malaise, fever, weight loss, organomegaly, and lymphadenopathy.
  • A child with involvement of two or more organ systems and no iatrogenic cause should be evaluated for defects in the interferon γ;/interleukin 12 pathway.
• Pulmonary disease represents the most common NTM infection in industrialized countries. MAC organisms are most commonly involved in North America. Pts present with months or years of throat clearing, nagging cough, and slowly progressive fatigue. M. kansasii can cause a TB-like syndrome, with hemoptysis, chest pain, and cavitary lung disease.
• Isolated cervical lymphadenopathy is the most common NTM infection among young children in North America and is most frequently caused by MAC organisms. The nodes are typically firm and painless and develop in the absence of systemic symptoms.
• Skin and soft-tissue disease usually requires a break in the skin for introduction of the organism. Different NTM species are associated with specific exposures.
  • M. fortuitum is linked to pedicure bath-associated infections, particularly if skin abrasion (e.g., during leg shaving) has immediately preceded the pedicure.
  • Rapidly growing NTM are associated with outbreaks of infection acquired via skin contamination from surgical instruments (especially in cosmetic surgery), injections, and other procedures. These infections are typically accompanied by painful, erythematous, draining SC nodules, usually without associated fever or systemic symptoms.
  • M. marinum can be acquired from fish tanks, swimming pools, barnacles, and fish scales. Pts typically develop papules or ulcers (“fish-tank granuloma”) that can progress to tendonitis and tender nodules on the arm in a pattern similar to that caused by Sporothrix schenckii. Lesions appear days or weeks after acquisition of the organism.
  • M. ulcerans is a waterborne organism found primarily in tropical areas, especially in Africa. Skin lesions are typically painless, clean ulcers that slough and can cause osteomyelitis.

Diagnosis

Similar to M. tuberculosis, NTM can be detected on acid-fast or fluorochrome smears of clinical samples and can be cultured on mycobacterial medium. Isolation of NTM from a clinical specimen may reflect colonization and requires an assessment of the organism's clinical significance.

• Isolation of NTM from blood specimens is clear evidence of disease; many NTM species require special media and will not grow in standard blood culture medium.
• The American Thoracic Society has published guidelines for the diagnosis of pulmonary NTM disease that require the growth of NTM from two of three sputum samples, a positive bronchoalveolar lavage sample, or a pulmonary parenchyma biopsy sample with granulomatous inflammation or mycobacteria found on section and NTM in culture. Although these guidelines are specific to MAC, M. abscessus, and M. kansasii, they probably apply to other NTM as well.
• The only antibiotic susceptibility assessment indicated is testing of MAC organisms for susceptibility to clarithromycin and of M. kansasii for susceptibility to rifampin.