An infection caused by two closely related and hard-to-distinguish bacteria, Mycobacterium avium and Mycobacterium intracellulare. These two bacteria can be found in drinking water, dirt, and household dust. Most people are not affected by the bacteria, but for people with severely weakened immune systems, the bacteria can cause infection. M. intracellulare tends to cause lung disease, and M. avium tends to spread throughout the body (disseminated). Symptoms of disseminated Mycobacterium avium-intracellulare (MAI) infection include fever, night sweats, weight loss, abdominal pain, fatigue, and diarrhea. In people infected with HIV, MAI infection that is outside of the lungs (extrapulmonary) or that has disseminated is an AIDS-defining condition.