DESCRIPTION

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.
• 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.
• NTMB’s biofilm-forming capabilities within aqueous environments contribute not only to its transmission but also its increased difficulty of eradication.
• NTMB may also be referred to as mycobacteria other than tuberculosis (MOTT) or atypical mycobacteria (ATM).
• Mycobacterium avium complex (MAC) encompasses multiple species including M. avium and Mycobacterium intracellulare, the most well-known species in this complex.

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 almost 200 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 biopsy, surgical procedure, tattoos, injections, or piercing as well as from an open or contaminated wound.
• Opportunistic pathogens that pose a greater risk to persons with chronic lung disease or immune compromise

ETIOLOGY

• 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 MAC.
• In healthy adults, pulmonary disease is the most common illness, typically caused by MAC, 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, pneumonia, and disseminated disease.
• Disseminated disease is seen primarily with MAC in patients with impaired cell-mediated immunity.

RISK FACTORS

• Factors that are associated with an increased risk of NTMB disease are as follows:
  • 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 MAC cervical adenitis.

GENERAL PREVENTION

• Discourage cleaning of medical hardware or contaminated wounds with tap water.
• Follow sterilization guidelines for disinfection of surgical equipment.
• Health care facilities should have water management programs to reduce risk of infection.

PATHOPHYSIOLOGY

• 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 M. avium complex and M. kansasii, take >7 days and typically 4 to 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.
• Infections are almost always environmental, although person-to-person spread of M. abscessus has been reported in patients with cystic fibrosis.

COMMONLY ASSOCIATED CONDITIONS

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