[Non tuberculous mycobacterial diseases]

Mycobacteria species other than members of Mycobacterium tuberculosis complex are called non tuberculous mycobacteria (NTM) or "atypical" mycobacteria. To date, about 80 mycobacterial species have been described. They are usually opportunistic pathogens with variable degrees of virulence. Tuberculosis is the commonest mycobacterial disease in the world, followed by leprosy and Buruli ulcer. Before the AIDS epidemic, NTM diseases were confined to the lungs (M. kansasii, M. intracellulare and M. avium), the skin (M. marinum) or cervical lymph nodes (M. scrofulaceum). The outbreak of AIDS epidemic has dramatically changed the epidemiology of NTM diseases. Between 25 to 50% of AIDS patients in Europe and USA are infected with NTM. NTM infections are usually disseminated in patients with profound immunodeficiency. The inflammatory response and the prognosis of NTM diseases depend on the immunological status and the NTM species. Diagnosis may be difficult, especially in AIDS patients in whom numerous diseases are often associated. Diagnostic criteria involve clinical, radiological, microbiological and pathological findings. Identification of Mycobacterium species in cultures is the gold standard. Pathological examination has several interests: it may reveal an NTM disease, it provides a more rapid assessment of the infection than cultures, and helps to evaluate the virulence of NTM species identified by cultures.