Abstract
Despite recent highly significant publications, attempts to develop evidence-based guidelines and meta-analyses in the field of environmental risks in hospital all come up against the feebleness of existing causal links. This article expounds and discusses the hypothesis that our understanding of the mechanisms involved in the transmission of healthcare associated infection (HAI) could be improved by progressively taking into account the complexity of microbial ecology in hospitals, and thus lead to the creation of reasonable and robust prevention measures to implement. This non-exhaustive clarification raises several issues : 1) the existence, within the species of bacteria responsible for HAI, of bacterial ecotypes specific to hospital ecosystems, patient included; 2) the part played by the variability and biodiversity of hospital pathogens in their successful outbreaks and implantation thanks to a “collective insurance”; 3) a paradigm shift with the entire pathogen population of the patient and his close hospital environment being considered as the nosocomial transmission units rather tha just the isolated pathogenic strains ; 4) how relevant is the current mode of microbiological environmental monitoring ? The challenge today is to confront microbiological data to clinical epidemic situations in order to determine clinical environmental indicators allowing an accurate determination of infection risks.