Bacterium
Mycobacterium avium complex
Nontuberculous mycobacteria; disseminated in advanced HIV
my-koh-bak-TEER-ee-um AY-vee-um
High-yield clue
Disseminated MAC is a classic opportunistic infection of advanced HIV with CD4 counts under 50, presenting with fever, weight loss, and positive blood cultures.
Overview
A group of environmental nontuberculous mycobacteria (M. avium and M. intracellulare) that act as opportunistic pathogens. They are the classic teaching cause of disseminated infection in advanced HIV.
Classification
- Acid-fast bacilli
- Nontuberculous mycobacteria
- Slow-growing
- Environmental (water/soil)
- M. avium + M. intracellulare
Lab & identification clues
- Acid-fast staining
- Blood culture for disseminated disease
- Environmental water/soil source
- Slow-growing colonies
Associations
- Disseminated disease in advanced HIV (CD4 under 50)
- Pulmonary disease in older adults / chronic lung disease
- Cervical lymphadenitis in children
Commonly confused with
- Mycobacterium tuberculosis
- Mycobacterium leprae
Your notes
Original student-study summary. Sources checked: OpenStax Microbiology 2e, NCBI Bookshelf Medical Microbiology, and CDC topic pages where applicable; reviewed 2026-06. Educational only; no diagnosis, treatment, dosing, or specimen-handling guidance.