is not always known. The Mycobacterium avium complex (MAC) includes common atypical bacteria, i.e. nontuberculous mycobacteria (NTM), found in the environment which can infect people with HIV and low CD4 cell count (below 100/microliter); mode of infection is usually inhalation or ingestion. MAC causes disseminated disease in up to 40% of people with HIV in the United States, producing fever, sweats, weight loss, and anemia. Disseminated MAC (DMAC) characteristically affects people with advanced HIV disease and peripheral CD4 cell counts less than 50 cells/uL. Effective prevention and therapy of MAC has the potential to contribute substantially to improved quality of life and duration of survival for HIV-infected persons. Pathophysiology MAC is the most commonly found form of NTM. Immunodeficiency is not a requirement for MAI. MAC usually affects patients with abnormal lungs or bronchi. However, Jerome Reich and Richard Johnson describe a series of six patients with MAC infection of the right middle lobe or lingula who did not have any predisposing lung disorders. The right middle lobe and lingula of the lungs are served by bronchi that are oriented downward when a person is in the upright position. As a result, these areas of the lung may be more dependent upon vigorous voluntary expectoration (cough) for clearance of bacteria and secretions. Since the six patients in their retrospective case series were older females, Reich and Johnson proposed that patients without a vigorous cough may develop right middle lobe or left lingular infection with MAC. They proposed this syndrome be named Lady Windermere syndrome, after the character Lady Windermere in Oscar Wilde's play Lady Windermere's Fan. However, little research has confirmed this speculative cause. Diagnosis Diagnosis can be achieved through blood cultures or cultures of other bodily fluids such as sputum. Bone marrow culture can often yield an earlier diagnosis but is usually avoided as an initial diagnostic step because of its invasiveness. Many people will have anemia and neutropenia if the bone marrow is involved. MAC bacteria should always be considered in a person with HIV infection presenting with diarrhea. The diagnosis requires consistent symptoms with two additional signs: Chest X-ray or CT scan showing evidence of right middle lobe (or left lingular lobe) lung infection Sputum culture or bronchoalveolar lavage culture demonstrating the infection is caused by MAC Disseminated MAC is most readily diagnosed by one positive blood culture. Blood cultures should be performed in patients with symptoms,