Mycobacterium avium-intracellulare infection

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. 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. 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. The treatment of choice is surgical excision of the affected lymph nodes, with antibiotic treatment (usually clarithromycin and rifabutin for 18 to 24 months) reserved for those patients who cannot have surgery. MAC bacteria are common in the environment and cause infection when inhaled or swallowed. Recently, M. avium has been found to deposit and grow in bathroom shower heads from which it may be easily aerosolized and inhaled.