Invasive Methicillin-Resistant Staphylococcus aureus Infections Among Dialysis Patients --- United States, 2005

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Staphylococcus aureus is a leading cause of bloodstream and other invasive infections in the United States. S. aureus has become increasingly resistant to first-line antimicrobial agents in health-care settings.^[1] Dialysis patients are especially vulnerable to infections, frequently those caused by antimicrobial-resistant organisms, including methicillin-resistant Staphylococcus aureus (MRSA). To assess the incidence of invasive MRSA infection among dialysis patients in the United States during 2005, surveillance data were analyzed from the Active Bacterial Core surveillance (ABCs) system. This report summarizes the results of that analysis, which estimated that, in 2005, the incidence of invasive MRSA infection among dialysis patients was 45.2 cases per 1,000 population. Persons receiving dialysis are at high risk for infection with invasive MRSA compared with the general population, in which rates of invasive MRSA have ranged from 0.2 to 0.4 infections per 1,000 population.^[2] The findings in this report underscore the need for continued surveillance and infection-control strategies aimed at reducing infection rates and preventing additional antimicrobial resistance among persons receiving dialysis.

ABCs, part of CDC's Emerging Infections Program, conducts ongoing, active, population-based surveillance for invasive pathogens, including MRSA, in selected areas of the United States. In 2005, the entire state of Connecticut and 23 counties in eight other states (California, Colorado, Georgia, Maryland, Minnesota, New York, Oregon, and Tennessee) monitored MRSA infections. A case was defined as a positive MRSA culture from normally sterile sites (e.g., blood, cerebrospinal fluid, joint fluid, or pleural fluid) occurring in a patient residing in the ABCs surveillance area. Surveillance staff collected demographic and clinical data from patient records and reported the data to CDC. All cases of invasive MRSA reported during 2005 were used to calculate incidence rates. Demographic and outcome data were analyzed from case reports obtained during July 2004-June 2006. The analysis was limited to cases occurring in patients with a history of peritoneal dialysis or hemodialysis during the preceding 12 months; recurrent cases were excluded. The number of dialysis patients was obtained for Connecticut and the 23 counties from the United States Renal Data System dialysis population count (as of December 31, 2004) for use as denominators; 2005 denominators were not yet available.^[3]

Laboratories voluntarily submitted isolates from cases, and a subset of isolates was collected for microbiologic characterization at CDC. A total of 126 isolates were obtained from dialysis patients. Isolates were tested by pulsed-field gel electrophoresis (PFGE) and were grouped into types using Dice coefficients with 80% relatedness. Isolates with pulsed-field types USA300, USA400, USA1000, or USA1100 are obtained primarily from community infections and are considered to be of community origin; those with types USA100, USA200, and USA500 are predominantly from health-care-associated infections and are considered to be of health-care origin.^[4]

Of the 5,287 cases of invasive MRSA reported from ABCs sites during 2005, a total of 813 (15.4%) occurred in dialysis patients. Overall incidence of invasive MRSA infection among dialysis patients was 45.2 cases per 1,000 dialysis population, indicating a 100-fold higher risk than for the general population ( Table 1 ). The rate varied by ABCs site, from 27.2 in California to 92.0 in Maryland. During July 2004-June 2006, approximately 70% of invasive MRSA infections among dialysis patients occurred in persons aged >50 years. Males and blacks accounted for 57% and 56%, respectively, of the total population of dialysis patients with these infections. The majority (86%) of the infections were bloodstream infections, identified via positive blood culture. Approximately 85% of dialysis patients had an invasive device or catheter in place at the time of infection, and approximately 90% required hospitalization. The in-hospital mortality rate for MRSA-related hospitalization was 17%.

Of the 126 MRSA isolates obtained from dialysis patients, 80% of the strains were of health-care origin, with USA100 representing 92% of the health-care strains and 74% of all isolates obtained. Community strains accounted for approximately 14% of the strains detected in dialysis patients, with USA300 accounting for 89% of the community strains and nearly 13% of all dialysis isolates. Six percent of the isolates either did not match existing USA strains within 80% or were classified as other non-USA strains. Antibiotic susceptibility results were reported for 113 MRSA isolates from dialysis patients. None of the isolates were resistant to vancomycin, daptomycin, or linezolid.

Morbidity and Mortality Weekly Report. 2007;56(9):197-199. © 2007 Centers for Disease Control and Prevention (CDC)

Cite this: Invasive Methicillin-Resistant Staphylococcus aureus Infections Among Dialysis Patients --- United States, 2005 - Medscape - Mar 09, 2007.