An infection caused by a group of bacteria called Mycobacterium avium complex (MAC). MAC include Mycobacterium avium, Mycobacterium intracellulare, and other similar Mycobacteria. MAC bacteria can be found in drinking water, dirt, and household dust. MAC infection usually starts in the lungs and intestines, but can spread throughout the body (disseminated). Symptoms of disseminated MAC infection include fever, night sweats, weight loss, abdominal pain, fatigue, and diarrhea. Most people with healthy immune systems are not affected by the bacteria. In people infected with HIV, MAC infection that is outside of the lungs (extrapulmonary) or that has disseminated is an AIDS-defining condition.