Criteria for the diagnosis of infection by an atypical mycobacterium include repeated isolation of a potentially pathogenic species, the absence of other pathogens, and a compatible clinical, radiologic, or pathologic picture. The mode of acquisition of M. avium complex in patients with AIDS is not clear. Systemic symptoms predominate, including fever, chills, night sweats, and profound weight loss. Gastrointestinal symptoms, such as diarrhea and malabsorption, are often prominent. Disseminated M. avium complex infection can be readily documented by mycobacterial smears and cultures in AIDS patients.
Organisms are frequently present in the lungs, liver, spleen, bone marrow, and lymph nodes.
Intestinal or pulmonary infection may precede M. avium complex bacteremia, but smears and cultures of these sites are not sensitive enough to be used as screening tests for early infection. The management of M. avium complex has improved greatly. New antimicrobials are effective for chemoprophylaxis. The drugs are equally efficacious, but azithromycin is often preferred for its greater convenience. Rifabutin is an alternative prophylactic agent for patients who cannot tolerate a macrolide.