[Nosocomial infections: definition, frequence and risk factors]

Infection is nosocomial if it missed at the time patient admission in the health establishment. When infectious status of the patient on admission is unknown, infection is generally regarded as nosocomial if it appears after a time of at least 48 hours of hospitalization. For surgical site infection, the commonly allowed time is 30 days, or, in case of prosthesis or an implant, one year after surgical intervention. Nosocomial infections (NI) constitute major health care problem from their frequency, their cost, their gravity. Mortality related to NI can attempt 70% in certain units like intensive care units. Two ways of contamination are possible: the endogenous way is responsible of majority of hospital infections. The normally sterile sites are contaminated then colonized by the flora which is carrying the patient himself, with the favor of a rupture of the barriers of defense. The exogenic way is associated colonization, possibly followed by infection, of the patient by external bacteria, coming from others patients or from environment, transmitted in an indirect way (aerosols, manuportage, materials). Whatever its mode of transmission, apparition of nosocomial infection can be related to several supporting factors: age and pathology, certain treatments (antibiotic which unbalance patients' flora and select resistant bacteria, immunosuppressive treatments), invasive practices necessary to the patient treatment. The prevalence of nosocomial infections is higher in the intensive care units where certain studies bring back rates of 42.8% versus 12.1% in others services. The four sites of nosocomial infection most frequently concerned are: the respiratory site, urinary infections, bloodstream infections (Catheters related bloodstream infections in particular), and surgical sites infections. The relative proportion of these infections varies according to principal activity of the unity.