Mycobacterium avium complex (MAC) infection is caused by the Mycobacterium avium complex (M. avium and M. intracellulare). It more commonly occurs in patients with advanced immunosuppression and is considered an AIDS-defining condition. Diagnosis is based on isolation of the organism (acid-fast bacilli) on culture and treatment consists of at least two anti-mycobacterial drugs (e.g., a macrolide with ethambutol).
- Caused by the Mycobacterium avium complex, which consists of the ubiquitous pathogens M. avium and M. intracellulare.
- AIDS-defining condition; frequent opportunistic bacterial infection in patients with AIDS
- Infection occurs via the gastrointestinal or respiratory epithelium through inhalation, ingestion, or inoculation.
- Bacteria may remain confined to the area of entry (localized) or spread via the lymphatic system and the blood (disseminated).
Diagnosis of disseminated MAC is based on isolation of the organism in a patient with characteristic clinical features. 
- Laboratory studies
- Imaging: depends on the presenting symptoms; examples include
- Initial regimen 
- Optional third and fourth drugs