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Mycobacterium avium Complex

Mycobacterium avium complex (MAC), a disease caused by Mycobacterium avium or Mycobacterium intracellulare, has become one of the major systemic bacterial infections associated with AIDS. MAC usually complicates the later stages of AIDS when the immune system is nearly nonexistent, and it accounts for more than 95 percent of mycobacterial infections caused by pathogens other than Mycobacterium tuberculosis, the pathogen responsible for tuberculosis (TB; see Tuberculosis). It is estimated that MAC will occur in approximately one-third of patients with AIDS in the United States. In approximately 8 percent of patients, MAC is the AIDS-defining illness.