Mycobacterium intracellulare

MAC is ubiquitous in soil and water and is acquired by inhalation or ingestion rather than person to person. In advanced HIV with CD4 below 50 it disseminates, producing prolonged fever, night sweats, weight loss, diarrhoea, hepatosplenomegaly, anaemia, and a markedly raised alkaline phosphatase, with foamy macrophages stuffed with acid-fast bacilli on marrow or liver biopsy. Prophylaxis with azithromycin was historically given below 50 cells but is now often omitted if effective antiretroviral therapy is started promptly. In HIV-negative patients MAC causes two pulmonary syndromes: cavitary upper lobe disease in older men with COPD, and nodular bronchiectasis of the right middle lobe and lingula in older non-smoking women, the so-called Lady Windermere syndrome, attributed to habitual cough suppression. Treatment requires prolonged multidrug therapy with a macrolide plus ethambutol and a rifamycin, continued for at least twelve months after culture conversion; macrolide monotherapy must be avoided because resistance develops rapidly.