Mycobacterium avium complex

Organism

 * Mycobacterium avium
 * Mycobacterium intracellulare

Epidemiology
Most common in patients infected by HIV.

Transmission: Organisms are found ubiquitously in the soil and presumably taken in through inhalation or ingestion. Does not appear to be communicable; no isolation is required.

Risk Factors: There is a demonstrably increased risk as the CD4 count drops below 50. A less correlative factor is recent granulocyte stimulating factor administration.

Pathogenesis
Thought to represent active acquisition rather than reactivation like other opportunistic infections.

Portals of entry include respiratory and gastrointestinal tract with dissemination via the lymphatics.

Clinical Presentation
Usually presents as disseminated disease. May present in a more limited manner in patients on HAART.

Disseminated Disease
Symptoms: Fever, night sweats, abdominal pain, diarrhea, and weight loss (before fever).

Laboratory Findings: Anemia, elevated alkaline phosphatase, elevated lactate dehydrogenase.

Diagnostic step: Isolate MAC from the blood.

Localized Disease
Symptoms: Focal lymphadenitis, fever, focal inflammation in a lymph node

Laboratory Findings: Leukocytosis, sterile blood cultures.

Diagnostic step: Aspirate culture or aspiration of a lymph node.

Effect on HIV infection
Small significant increase in HIV RNA levels.

Diagnosis
Make the diagnosis of MAC by isolation of organism in blood culture or lymph node. The time required for positive cultures is extensive: bone marrow takes approximately 22 days, blood culture