Description

Nontuberculous mycobacteria (NTMB) are mycobacteria other than the Mycobacterium tuberculosis complex bacteria (M. tuberculosis, Mycobacterium africanum, Mycobacterium bovis, Mycobacterium canettii, 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.
• Runyon classification was used priorly to classify NTMB and still may be referenced in literature.
• Disease from these infections most commonly presents as cervical lymphadenitis in children.
  • Pulmonary, disseminated skin or soft tissue diseases are other possible forms of NTMB infections present in adolescents.
• NTMB’s biofilm-forming capabilities within aqueous environments contributes not only to its transmission but also to its increased difficulty of eradication.
• NTMB may also be referred to as mycobacteria other than tuberculosis (MOTT).

Epidemiology

• NTMB are ubiquitous in nature and may be found in soil, food, water, and animals.
  • Both fresh and tap water sources are NTMB reservoirs as well with the later serving as the most common source for humans.
• Although more than 130 species of mycobacteria have been identified, not all have been shown to cause disease in humans.
• 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.
• NTMB can gain entry through a person’s skin via various modes of exposure.
  • Some examples include following a pedicure, punch biopsies, surgical procedure, tattoos, injections, or piercing as well as from an open or contaminated wound.

Risk Factors

• Factors that are associated with an increased risk of NTMB disease are as follow:
  • Cystic fibrosis
  • Primary ciliary dyskinesia
  • Immune deficiency, especially HIV
  • Tympanostomy tubes
  • Foreign bodies or medical hardware
  • Interleukin-12 receptor deficiency
  • Interferon-γ receptor defects
  • Immunosuppressive therapies
• Factors that are associated with a decreased risk of NTMB disease are as follows:
  • Bacillus Calmette–Guérin (BCG) vaccination
    • Children vaccinated with BCG have shown a decreased risk of Mycobacterium avium complex (MAC) cervical adenitis.

General Prevention

• Discourage cleaning of open or contaminated wound with tap water.
• Recommended sterilization guidelines followed for disinfection of surgical equipment

Pathophysiology

• 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

Etiology

• Rapid growers include the M. fortuitum and Mycobacterium chelonae/abscessus groups. These rapid growers show significant growth on culture media in 3 to 7 days.
• Slow-growing mycobacteria, such as MAC and Mycobacterium kansasii, take >7 days and typically 4 to 6 weeks to grow in culture.
• Cervical adenitis is the most common presentation in healthy children 1 to 5 years of age. In the United States, 80% of these cases are due to M. avium-intracellulare (MAI).
• In healthy adults, pulmonary disease is the most common illness, typically caused by MAI, M. 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.

Commonly Associated Conditions

• Coexisting primary or structural lung disease
• Scoliosis
• Pectus excavatum
• Diabetes mellitus