Mycobacterium avium-intracellulare infection (MAI) is an atypical mycobacterial infection, i.e. one with nontuberculous mycobacteria or NTM, caused by Mycobacterium avium complex (MAC), which is made of two Mycobacterium species, M. avium and M. intracellulare. This infection causes respiratory illness in birds, pigs, and humans, especially in immunocompromised people. In the later stages of AIDS, it can be very severe. It usually first presents as a persistent cough. It is typically treated with a series of three antibiotics for a period of at least six months. M. avium, M. intracellulare, and M. chimaera are each saprotrophic organisms present in soil and water; entry into hosts is usually via the gastrointestinal tract, but also can be via the lungs. MAC infections can cause fevers, diarrhea, malabsorption, as well as loss of appetite and weight loss, and can disseminate to the bone marrow. MAI is typically resistant to standard mycobacterial therapies. Signs and symptoms
Pulmonary involvement symptoms are similar to tuberculosis (TB), and include fever, fatigue, weight loss, and coughing up blood. Diarrhea and abdominal pain are associated with gastrointestinal involvement. Children
M. avium and M. haemophilum infections in children form a distinct clinical entity, not associated with abnormalities of the immune system. M. avium typically causes unilateral swelling of one of the lymph nodes of the neck. This node is firm at the beginning, but a collar-stud abscess is formed eventually, which is a characteristic blue-purple in colour with multiple discharging sinuses.
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 Wildes play Lady Windermeres 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.