Nontuberculous Mycobacterial Disease

Nontuberculous Mycobacterial (NTM) disease refers to infections caused by mycobacterial species other than Mycobacterium tuberculosis complex and M. leprae. These organisms are environmental pathogens that can cause pulmonary, lymphatic, cutaneous, or disseminated infections, particularly in immunocompromised hosts.

Definition

Epidemiology

Found worldwide; incidence increasing due to improved detection and immunosuppression prevalence.
More common in older adults, patients with structural lung diseases (COPD, bronchiectasis, cystic fibrosis), and immunocompromised individuals.
Mycobacterium avium complex (MAC) is the most common cause of NTM lung disease globally.
Other frequent pathogens include M. kansasii, M. abscessus, M. fortuitum, and M. chelonae.
Transmission is environmental — through inhalation, ingestion, or inoculation; human-to-human spread is extremely rare.
No known animal reservoir; organisms commonly found in soil and water systems.

Etiology

Causative agents: various species of NTM, notably:
— Mycobacterium avium complex (MAC)
— Mycobacterium kansasii
— Mycobacterium abscessus
— Mycobacterium fortuitum
— Mycobacterium chelonae
Environmental exposure (soil, water, dust) is the main route of infection.
Predisposing factors: chronic lung disease (COPD, bronchiectasis), cystic fibrosis, previous tuberculosis, immunosuppression (HIV, corticosteroids, transplant), and body habitus (tall, thin, older women with scoliosis or pectus excavatum).

Pathophysiology

NTMs are opportunistic pathogens that infect through respiratory or skin entry points.
Once inhaled or inoculated, they survive within macrophages by inhibiting phagosome-lysosome fusion.
Granulomatous inflammation develops, leading to tissue destruction and caseating or non-caseating granulomas.
In pulmonary disease, chronic infection causes bronchiectasis and cavitary lesions similar to tuberculosis.
Disseminated infection occurs in immunocompromised patients (especially AIDS) due to hematogenous spread.