| Nontuberculous Mycobacterial Infections Definition - The nontuberculous mycobacteria (NTM) encompass the mycobacterial species other than organisms of the Mycobacterium tuberculosis complex and M. leprae.
- More than 100 mycobacterial species have been identified.
- Traditionally identified by their slow growth and acid-fast staining (they do not lose their color with acidified alcohol after staining with either auramine-rhodamine or carbol-fuchsin)
- Main species include:
- M. avium
- M. intracellulare
- M. kansasii
- M. abscessus
- M. chelonae
- M. fortuitum
- M. marinum
- M. ulcerans
- Most species are less virulent for humans than is M. tuberculosis.
- Symptomatic infections are often associated with local or generalized defects in host defenses, such as HIV infection/AIDS.
- The NTM are typically acquired from environmental sources and thus are also referred to as environmental mycobacteria.
- Widely distributed in water, biofilms, and soil as well as in numerous animal species
 Epidemiology - Asymptomatic infections with NTM are common in humans.
- Probably acquired most often in childhood
- 30–40% of adults in the northern and southern U.S. have had prior unrecognized or asymptomatic infection.
- Most often caused by organisms of the M. avium complex (MAC)—i.e., M. avium, M. intracellulare, and genetically related unnamed species
- Pulmonary disease due to MAC
- MAC is more common than M. tuberculosis as a cause of mycobacterial pulmonary disease among persons born in the U.S.
- Marked increase in incidence of MAC infection over past 2–3 decades
- Primary disease occurs in apparently healthy nonsmokers.
- Age: >50 years
- Sex: Females > males
- Secondary disease occurs in patients with preexisting pulmonary disease.
- Age: 30–70 years (mean, 60 years)
- Sex: Males > females
- Pulmonary disease due to M. kansasii
- Many areas of the world, including North America, Europe, and South Africa
- In the U.S.:
- Second most common cause of lung disease due to NTM
- Distributed largely in central and southern states and California
- Cutaneous M. ulcerans ("Buruli ulcer")
- Endemic regions: Central and West Africa, Central and South America, Malaysia, Indonesia, Papua New Guinea, Australia
Risk Factors - Risk factors for infection
- Exposure to contaminated source
- Cutaneous disease outbreaks associated with contaminated injections, body piercing, etc.
- Risk factors for secondary pulmonary disease due to MAC
- Risk factors for pulmonary disease due to M. kansasii
- Chronic obstructive pulmonary disease
- Carcinoma of the lung
- Silicosis
- Prior tuberculosis
- Associated with poverty
- Risk factors for pulmonary disease with M. abscessus, M. chelonae, and M. fortuitum
- Underlying pulmonary disease (e.g., cystic fibrosis)
- Risk factors for disseminated disease
- Impaired cellular immunity
- Advanced HIV disease
- Treatment with glucocorticoids or other immunosuppressive agents (e.g., for organ transplantation)
- Leukemia (especially hairy cell leukemia)
- Lymphoma
- Heritable disorders of interferon-γ production and function
Etiology - Caused by NTM
- NTM have conventionally been characterized by the time required for growth on solid media (see Laboratory Tests).
- Rapidly growing NTM species appear within 7 days.
- M. abscessus, M. fortuitum, M. chelonae
- Water, soil, and nosocomial sources of infection
- Slow-growing species require 2–3 weeks to grow on solid media.
- Require special solid media
- Automated broth systems may permit isolation within 10–14 days.
- Usually isolated only when cultures for mycobacteria are specifically requested
- Environmental reservoirs
- M. avium: hot-water systems, natural water, soil
- M. intracellulare: hot-water systems, natural water, soil
- M. kansasii: potable and natural water
- M. marinum: fish tanks, salt water
- M. ulcerans: natural water
- NTM are acquired via exposure to contaminated soil, water, and possibly animals by routes that include:
- Cutaneous
- Respiratory
- GI
- Parenteral (rare)
- Pathogenesis
- NTM are ingested by host macrophages and may survive within these cells to replicate and cause symptomatic infection.
- Disease manifestations in immunocompetent hosts are due to host cellular immune responses and the formation of granulomas.
- Deficiencies in CD4+ T cell function due to HIV infection and inherited deficiencies in the production of or response to interferon-γ are associated with disseminated NTM infection.
Associated Conditions - Accumulating data support an association between Crohn’s disease and infection with M. avium subspecies paratuberculosis.
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