Emerging Issues

The current recommendations for IE prophylaxis are based on an epidemiology in which VGS were the predominant pathogens. Recent studies have demonstrated that S. aureus has become the major cause of IE [130]. An increasing proportion of cases of S. aureus bloodstream infection and IE is acquired nosocomially or nosohusially (i.e., health-care-associated) [130-132], due to increasing use of intravascular devices (e.g., central venous catheters, dialysis catheters, prosthetic vascular grafts, pacemakers/ defibril-lators). These devices can also permit coagulase-negative staphylococci (CoNS, e.g., S. epidermidis) to establish endovascular infections. Indeed, the incidence of CoNS IE is also increasing [133]. The existing aminopenicillin-based prophylaxis recommendations are not likely to be effective in preventing S. aureus IE, based on in vitro susceptibility testing in which <5% of clinical isolates are inhibited by penicillin [134-136]. Similarly, they are not expected to be effective against CoNS. There are currently no national guidelines regarding IE prophylaxis for the above-mentioned procedures. The recommendations that exist recommend prophylaxis to minimize the risks of intraoperative contamination and surgical site infection [137]. Typically a first-generation cephalosporin directed primarily against staphylococci is administered in the peri-implantation time period for clean-contaminated procedures, and only for a short duration (e.g., a few doses) [137]. This approach, however, may not be adequate to prevent bac-teremia. For devices in which a portion remains external to the patient, and thus provides a persistent portal of entry, the brief administration of the peri-procedure prophylaxis is certainly not sufficient to prevent bacteremic episodes that may occur during the lifespan of the implanted device. In particular, the use of central venous catheters (CVCs) has emerged as a major risk factor for bacteremia and IE [132]. Consequently, health-care-associated IE (HA-IE), defined as acute IE occurring 48-72 hours or more post-admission to hospital and/or IE directly relating to a hospital-based procedure performed during a previous hospital stay within eight weeks of admission, currently accounts for approximately 7.5-29% of all cases of IE seen in tertiary hospitals [138]. As such, modification of IE prophylaxis recommendations is required to address this changing epidemiology. One intervention which may be particularly useful for preventing CVC colonization, and therefore may minimize the risk of bacteremia and IE, is the antibiotic lock technique. This technique consists of filling and closing of the catheter lumen with a high-concentration antibiotic solution that acts locally to eradicate catheter-associated bacteremia, but that allows the side effects and toxicity associated with systemic administration of antibiotic to be avoided. Future studies are required before such intervention can be recommended.

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