Disease Due to the Mycobacterium avium Complex in Patients with AIDS: Epidemiology and Clinical Syndrome

Infection due to the Mycobacterium avium complex (MAC) is the most common opportunistic disease of bacterial origin among patients with AIDS in the United States. The incidence of disseminated disease due to MAC (DMAC) has risen dramatically in recent years. The risk of developing DMAC increases as the CD4+ lymphocyte count declines to < 100/mm3. Preliminary analyses of several studies suggest that gender, racial or ethnic group, and individual risk factors for human immunodeficiency virus infection do not influence the incidence of DMAC but that prior Pneumocystis carinii pneumonia, the development of severe anemia, or the interruption of antiretroviral therapy may increase risk. Both the respiratory and the gastrointestinal tracts probably serve as portals of entry for MAC. Colonization may potentiate the risk of DMAC but does not always precede dissemination. Patients with AIDS and DMAC have a shorter duration of survival than do those with AIDS but without DMAC. While treatment for DMAC may extend survival, no well-controlled, prospective, randomized clinical trial has documented this point. Most patients with AIDS and DMAC have disseminated multiorgan disease; the most frequently described symptoms include fever, night sweats, weight loss or wasting, diarrhea, and abdominal pain. The most commonly identified laboratory abnormalities are anemia and elevated serum levels of alkaline phosphatase. Localized disease syndromes related to MAC infection occur less often.