[New infectious risks].

New infectious risks have been identified or better elucidated in the last few years. The concept of infectious risks implies: a receptive host; or more or less pathogenic agent, inducing pathologic phenomena with variable facility, depending the receptivity of the host; and individual or community environmental factors (risk of accidental and massive contact with a pathogenic agent). These new risks are linked to: 1. the appearance of new or newly identified pathogenic agents, and the periodic changes in the pathogenic strength of some microorganisms, modifying the epidemiology of some infections; 2. changes in host receptivity (immunodepression, either acquired or linked to aggressive therapy which leads to prolonged survival of receptive patients); 3. environmental modifications (spread of resistant pathogenic bacteria, for example, presently the tuberculosis bacillus; declining socioeconomic conditions; reduced efficacy of community measures for prevention); 4. exposure to new risks linked to progress in diagnostic and therapeutic techniques (invasiveness of medical treatments, new treatment techniques, transplantations, implantation of foreign materials, transfusions). These phenomena illustrate the constant change in infectious risks and the need for a multidisciplinary approach to the problem and its effects.