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MRSA in Dialysis Patients
Abstract & Commentary
By Stan Deresinski, MD, FACP, Clinical Professor of Medicine, Stanford, Associate Chief of Infectious Diseases, Santa Clara Valley Medical Center, is Editor for Infectious Disease Alert.
Source: CDC. Invasive methicillin-resistant Staphylococcus aureus infections among dialysis patients - United States, 2005. MMWR. 2007;56:197-199.
Synopsis: The incidence of invasive infections due to MRSA in 2005 was approximately 100 times greater in chronic dialysis patients than in the general population.
Data collected by the Active Bacterial Core surveillance (ABCs) system in 2005 found that the incidence of invasive MRSA infections in patients undergoing dialysis was 45.2 per 1,000 population, an incidence far in excess of that estimated for the general population (0.2 to 0.4 per 1,000 population). This was based on active surveillance in entire state of Connecticut as well as in 23 counties in 8 other states. Cases were included in which MRSA was reported from any normal sterile site, including blood, cerebrospinal fluid, joint fluid, or pleural fluid. Thus, infections of the lung in cases in which the organism was recovered only from sputum were not included in this report.
Dialysis patients accounted for 813 (15.4%) of the more than 5,000 cases of invasive MRSA infection identified by ABCs sites during 2005. While the overall incidence, as indicated above, was 45.2 per 1,000 population, the incidence varied from a low of 27.2 at California locations to 92.0 per 1,000 population in Maryland. Patients > 50 years of age accounted for 70% of cases; 57% of patients were male and 56% were African-American. Bloodstream infections accounted for 86% of the sites infected. An invasive device or catheter was in place in approximately 85% of patients. Approximately 90% of patients were hospitalized and the in-hospital mortality was 17%.
Isolates that were available (n = 126) were examined by pulsed-field gel electrophoresis. By this technique, 80% belonged to types (USA100, USA200, USA500) that are associated with acquisition in the healthcare setting, with 92% of these being USA100. Of the 14% infections caused by MRSA types considered of community origin by molecular techniques (USA300, USA400, USA1000, USA1100), 89% were due to USA300. USA300 accounted for approximately 13% of all dialysis-related invasive MRSA infections.
As pointed out by the authors, in dialysis patients the incidence of invasive infections due to MRSA is the highest for any known population and approximately 100 times greater than in the general population. The importance of this is magnified by the fact that almost 14% of deaths in patients with end-stage renal disease are caused by infection, making this the second most frequent cause of mortality in these patients. S. aureus is the second most frequent cause of catheter-access-related bacteremia in dialysis patients, accounting for 29% of cases, just trailing coagulase-negative staphylococci (38%), but more frequent than Gram-negative bacilli (21%) and Gram-positive cocci other than staphylococci (10%).
The appropriate antibiotic choice in the management of hemodialysis patients with MRSA bacteremia is a matter of some discussion. There is increasing recognition of the inadequacies of vancomycin. Unfortunately, the remarkably frequent administration of vancomycin to chronic dialysis patients by nephrologists is also likely a contributing factor to the reported rise in its MICs to this organism ("MIC creep"), as well as to the detection of true VISA strains in this patient population. As implied by the authors, it also is not likely an accident that the first isolate of a fully vancomycin-resistant strain of S. aureus was recovered from a chronic hemodialysis patient. The use of an alternative therapeutic agent, such as daptomycin or linezolid seems preferable. In addition, the source of the infection should, if possible, be extirpated. More therapeutic choices may be available for the community-associated strains of MRSA, such as USA300, since they generally exhibit less multidrug resistance than do the classically hospital-based strains. Community-acquired MRSA (CAMRSA) have previously been identified as an increasing cause of infection in patients with end-stage renal disease by investigators at St. John Hospital in Detroit.1
Even more important is the issue of prevention. The incidence of invasive MRSA infection was more than 3 times more frequent in Maryland than in California, strongly suggesting that (in addition to the need for a better state nickname) nephrologists in the "Old Line State" may have much to learn from those in the "Golden State." Important to reducing the likelihood of infection due to antibiotic-resistant pathogens such as MRSA, is the need to slow the march of resistance by reducing the unnecessary use of antibiotics. In addition, the CDC has published recommendations, including standard infection control practices, for the prevention of transmission of infections among chronic hemodialysis patients.2 In chronic hemodialysis patients, the primary determinant of risk of bacteremia is the type of vascular access device used, with the greatest risk observed with catheters, the lowest with native arteriovenous fistulas, and an intermediate level of risk with grafts. As a consequence, avoiding the use of catheters may be the most important single means of reducing infection risk in these patients. Other methods may also be suggested by some recent findings. Thus, statin use was found in a large retrospective study to be associated with marked reduction in risk of hospitalization for sepsis in patients receiving chronic dialysis therapy.3 Similarly, aspirin therapy was associated with a decreased risk of S. aureus bacteremia in patients with tunneled catheters.4 Perhaps most important will be the development of a vaccine. While Staph VAX®, a bivalent vaccine containing S. aureus capsular polysaccharides 5 and 8 conjugated to nontoxic recombinant Pseudomonas aeruginosa exotoxin, initially appeared promising, its development is now on hold because of a failure to meet a primary endpoint in a large Phase III trial in 3,600 hemodialysis patients.5 While work is continuing in the development of other vaccine approaches, the availability of an effective vaccine will not be achieved any time soon.