[Epidemiology of nosocomial infections].

The frequency of nosocomial infections lies between 5 and 10%, and varies according to the type of hospital and service. Age, underlying disease invasive devices (such as catheters) or procedures are the main risk factors. Common nosocomial infections are urinary tract infections, pneumonia, surgical site infections, bacteremia/septicemia and intravascular catheter-related infections. Gram positive cocci and gram negative bacilli account for one third and two thirds of microorganisms respectively, Staphylococcus aureus being frequently resistant to antibiotics. Prevention is based on a better control of infection risk related to the use of invasive devices.