[Atypical mycobacterial skin infections]

The incidence of cutaneous atypical mycobacterial infections is increasing. Their clinical presentation is variable. The atypical mycobacteria are difficult to culture and thus diagnosis can be difficult to establish. PCR (Polymerase Chain Reaction) and mycolic acid analysis have recently been used for mycobacterial species identification, but are not routinely used. Risk factors for cutaneous atypical mycobacterial infection include (1) immunodepression due to HIV infection, lymphoma, leukemia or immunosuppressive therapy. Immunodepression is responsible for the emergence of cutaneous infections by a large variety of atypical mycobacterial species, particularly in industrialized countries. (2) The natural environment is directly responsible for the emergence of cutaneous infections but a small number of atypical mycobacterial species including M. marinum in Europe and North America, and M. ulcerans in the tropics. (3) The medical environment when sterilization is inadequate is also not uncommonly responsible. Clinical features are rarely specific for mycobacterial species, and thus analysis of factors relevant to treatment is more important than species classification. We describe environmental forms (Buruli ulcer caused by M. ulcerans is endemic in the tropics, and swimming pool granuloma which is the aquatic form of M. marinum infection), opportunist forms caused by various species in immunodepressed hosts and iatrogenic and accidental forms mostly due to M. fortiutum and M. chelonei. We review the literature and update the clinical characteristics and risk factors for these diseases.