Nontuberculous Mycobacterial Infections (Atypical Mycobacterial Infections)



Nontuberculous mycobacteria (NTMB) are mycobacteria other than the Mycobacterium tuberculosis complex bacteria (M. tuberculosis, Mycobacterium africanum, Mycobacterium bovis, Mycobacterium canetti, and Mycobacterium microti) or Mycobacterium leprae capable of causing disease in humans.

  • NTMB are classified based on growth rate in culture media as “rapid” or “slow” growers.
  • Disease from these infections most commonly presents as cervical lymphadenitis in children.


  • NTMB are ubiquitous in nature and found in soil, food, water, and animals.
  • More than 120 species of mycobacteria have been identified.
  • Each species has a different level of virulence and many species are associated with specific reservoirs or geographic areas. For example, Mycobacterium marinum is found in fish tanks and Mycobacterium malmoense is found in Northern Europe.
  • Health care–related infections can occur, typically due to rapid-growing Mycobacterium abscessus or Mycobacterium fortuitum.
  • Tap water is a major reservoir for a number of NTMB.

Risk Factors

  • Cystic fibrosis
  • Immune deficiency especially HIV
  • Tympanostomy tubes
  • Foreign bodies or medical hardware
  • Interleukin-12 receptor deficiency


  • Rapid growers include the M. fortuitum and Mycobacterium chelonae/abscessus groups. These rapid growers show significant growth on culture media in 3–7 days.
  • Slow-growing mycobacteria take more than 7 days and typically 4–6 weeks to grow in culture.
  • Dirty wounds and breaks in oral, respiratory, or gastrointestinal mucosa are the common portals of entry.
  • Infection is usually localized near the inoculation site and related regional lymph nodes.
  • No evidence of person-to-person spread


  • Cervical adenitis is the most common presentation in children 1–5 years of age. In the United States, 80% of these cases are due to Mycobacterium avium-intracellulare (MAI).
  • In healthy adults, pulmonary disease is the most common illness, typically caused by MAI, Mycobacterium kansasii, Mycobacterium xenopi, or M. malmoense.
  • Other presentations may include skin and soft tissue infections, bone and joint infections, chronic ear infections, catheter-associated infections, and pneumonia.
  • Disseminated disease is seen primarily with MAI in patients with advanced HIV.

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