[Epidemiological support in blood surveillance].

"Hémovigilance" is a continuous and standardized system for data collection and analysis, and diffusion of results to clinical and public health decision makers. This system has different objectives than clinical and epidemiological research on labile blood products. A published study of characteristics of donors that are infected by the human immunodeficiency virus illustrates the need for information on temporal patterns of events relevant to transfusion safety. Two cohort studies on post-transfusion hepatitis and a randomized study on cytomegalovirus infections illustrate the importance of surveillance for detecting events that are causally linked to transfusion. The interest of "hémovigilance" is also discussed in the context of epidemics and new hazards, when surveillance is the only possibility of designing ad-hoc epidemiologic studies, yielding results within delays compatible with decisions that are timely and effective for improving transfusion safety.