Risk factors and physiopathology of candidiasis.

Recent epidemiological surveys have demonstrated an important increase in nosocomial infections among which Candida sp. plays an increasingly prominent role. Candida is now involved in about 10% of all septicemia and leads to a very high mortality rate in immunodepressed patients. Clinical studies show that any modification of the host immune status can facilitate the proliferation of endogenous Candida which, according to the importance of the immune deficiency, can provoke diseases ranging from benign localized mucocutaneous candidosis to sometimes lethal systemic invasions. The pathogenic behavior of Candida cells is mainly due to a very high phenotypic biodiversity. Following even very slight environmental modifications, it may change its behavior through the appearance of new or amplified properties such as tube formation, adherence, protease secretion, etc. Together with the impairment of host defenses, these new invasive properties lead to the so-called opportunistic pathogenicity of Candida cells. From a host point of view, after the integrity of surface teguments, the mucosal protection is ensured by the Th1 "cellular" immune response which, through pro-inflammatory cytokine production, boosts the efficacy of the phagocytes (Polymorphonuclear cells and macrophages). Neutrophils are of particular importance as deep seated Candida proliferation is mostly associated with neutropenia. Whatever the pathogenic process, it is mostly due to modifications provoked by increasing medical awareness which makes patients more susceptible to illness. A better knowledge of the precise mechanisms involved and would lead to improved strategies for prevention.