Mycobacterium avium complex and atypical mycobacterial infections in the setting of HIV infection

Mark A. Jacobson, MD, University of California San Francisco, Judith A Aberg, MD, Washington University, Saint Louis

Mycobacterium avium complex (MAC) consists of several related species of mycobacterium that are ubiquitous in the environment.

MAC rarely causes disease in individuals with a normal immune system. In patients with AIDS, however, it is one of the most common serious opportunistic infections. Among HIV-infected individuals, disseminated MAC has historically occurred almost exclusively in patients with a CD4 count <50 cells/cu mm. Colonization of the respiratory or gastrointestinal (GI) tract by MAC can occur without evident morbidity; however, MAC colonization of these sites indicates that patients are at increased risk for developing disseminated MAC infection. Highly active antiretroviral therapy (HAART) has been associated with reductions in AIDS-related mortality, days of hospitalization, and the incidence of new OIs. However, there have been numerous reports of aberrant clinical presentations of MAC since the introduction of HAART.