Mycobacterium avium complex (MAC) is a group of bacteria commonly found in the environment, particularly in soil and water. It includes species like Mycobacterium avium and Mycobacterium intracellulare. These bacteria can cause infections, especially in individuals with weakened immune systems, such as those with HIV/AIDS or other conditions that impair immunity. In healthy individuals, MAC typically does not cause disease. However, when it does lead to infection, symptoms may include cough, fatigue, and weight loss. Diagnosis often involves laboratory tests, and treatment usually requires a combination of antibiotics over an extended period.