Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Mycobacterium avium complex is a group of genetically related bacteria belonging to the genus Mycobacterium. It includes Mycobacterium avium subspecies avium, Mycobacterium avium subspecies hominis, and Mycobacterium avium subspecies paratuberculosis. Historically, MAC has also included Mycobacterium avium intracellulare a distinct species of bacteria. MAC bacteria are common in the environment and cause infection when inhaled or swallowed. Symptoms of MAC diseases are reminiscent of tuberculosis. They include fever, fatigue, and weight loss.