Physiopathologie et épidémiologie des infections liées aux cathéters veineux centraux

Central venous-catheter related sepsis is the most frequent nosocomial infection, and is a particular problem in patients on long-term (home) parenteral nutrition. Infection rates range between 1 and 30 per 1.000 catheter days, depending on the type of vascular catheter and the clinical circumstances. Contamination of the infusate is rare, and contamination of the catheter is responsible for most device-associated infections. As a general rule, bacterial infection is secondary to infection of the subcutaneous tract of the catheter by the resident or transient skin flora at the entry site, or to contamination of the catheter hub-infusion tubing junction, especially when the system is frequently manupulated. Hematogenous seeding from a distant focus of infection may occur in intensive-care settings ; colonization of the catheter after bacterial intestinal translocation has been described in immunosuppressed patients. Several hospital - and patient - related risk factors, as well as catheter-related characteristics, can be used to optimize the indication, duration and management of the different devices presently available. Gram positive bacteria, especially coagulase-negative staphylococci, are the predominant pathogens, although other isolates can be encountered, according to the clinical circumstances and type of patient ; Candida infections are a particular and life-threatening problem in patients receiving TPN, and infections with opportunistic organisms have been reported in immunocompromised hosts. Bacterial attachement to the catheter, and possibly to the fibrin sheath within and around the catheter tip, is the initial step in the pathogenesis of catheter-related infections, followed by a significant colonization of the device and finally by clinical (local and/or systemic) infection. Process of adherence, colonization and infection exist in a sequential relashionship and depends, on one hand, on the degree of hydrophobicity of the bacterial strains and the available biopolymers, on the other hand on the production of an adherent biofilm by the infecting organisms, called "slime" or "glycoalyx" in the case of coagulase-negative staphylococci. This biofilm embeds bacteria on the surface of the catheter, thus creating a protective microenvironment which adversely affects host defenses and may act as a mechanical barrier to antibiotics. In future, the prevention of central venous catheter-related infections should be based on better understanding of host defense mechanisms in the vicinity of the devices, and on the production of new biocompatible materials that will not permit attachment and colonization by highly virulent strains of bacteria, especially coagulase-negative staphylococci.