Nosocomial infections with multidrug-resistant bacteria are increasing in ICU. They have major individual and collective consequences. Mortality in the ICU and prolongation of length of stay are the two main individual consequences known to date. Several confounding factors make it difficult to interpret studies, including the patient's underlying condition, the virulence of bacteria and the adequacy of therapy. It is essential to measure the share of each of these factors and to clarify their respective responsibilities to mobilize the different actors and improve the prognosis of patients in intensive care. In this thesis, and drawing upon a database including ICU patients, we used the latest statistical methods and tried to take into account the various confounding factors to evaluate the individual consequences of multidrug-resistant bacteria in ICU. We sought to address three specific questions: mortality linked to specific bacterial species, factors associated with mortality in patients with severe sepsis or septic shock in intensive care unit, and the consequences of the isolation of patients infected or colonized with multidrug-resistant bacteria. We demonstrated that (1) because they are associated with a longer stay in intensive care unit, Clostridium difficile infections increase the pressure of colonization although they have no direct consequence on mortality; (2) the prognosis of sever sepsis or septic shock depends on the adequacy of the antibiotic therapy and that resistant bacteria are often inadequately treated; and (3) that isolation is not only associated with an expected increase in the risk of nosocomial pneumonia with multi-drug resistant pathogens strains but also with an increase in non-infectious adverse events.
