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MRSA Central-Line Bacteremias Decline in U.S. ICUs
Abstract & Commentary
By Robert Muder, MD, Hospital Epidemiologist, Pittsburgh VA Medical Center, Section Editor, Hospital Epidemiology, is Associate Editor for Infectious Disease Alert.
Dr. Muder does research for Aventis and Pharmacia
Synopsis: Surveillance data from the CDC show that central-line associated bloodstream infections due to methicillin-resistant Staphylococcus aureus in U.S. intensive care units showed an overall decrease of 50% during 1997-2007. There was a concomitant decline in infections due to methicillin-susceptible S. aureus total central-line-associated BSIs during that period as well. The reason for this favorable change in infection rates is not ascertainable from the surveillance data.
Source: Burton DC et al. Methicillin-resistant Staphylococcus aureus central line-associated bloodstream infections in US intensive care units, 1997-2007. JAMA. 2009;301:727-736.
Data collected from the CDC's two surveillance systems1 for hospital-acquired infections tracked the rate of central-line-associated blood stream infections (CLA-BSIs) from 1997-2007. Data were not collected in 2005 during the transition between the two systems. A total of 1,684 ICUs reported CLA-BSI data to the CDC. The reporting facilities changed during the period, as facilities entered or left the program. Prior to 2007, the median number of facilities participating was 244; in 2007 the number increased to 518. The rate of MRSA CLA-BSI increased significantly from 1997 to 2001, from 0.3 to 0.4 cases per 1,000 central line days, then fell significantly from 2001 to 2007, reaching 0.2 cases per 1,000 central line days. The overall decline during the entire reporting period was 49.7%. During the entire 11-year reporting period, the rate of CLA-BSI due to methicillin-susceptible S. aureus declined steadily from 0.3 to 0.09 cases per 1,000 patient days, a 70% reduction. During the same period, there was a continuous and significant decrease in the rate of CLA-BSIs due to all pathogens; this decrease was consistent across ICU types.
To begin with, I have a quibble with the title. It would be more accurate to bill this as "central-line-associated bloodstream infections declined substantially. . .but the decline in MRSA infections took a bit longer." MRSA accounted for less than 10% of CLA-BSIs in the units studied, and the change in the rate of MRSA infection is a very small contributor to the overall change in the rate of CLA-BSIs.
Having said that, this report shows that CLA-BSIs are clearly decreasing in ICUs — at least among those reporting through NNIS and, later, NHSN. There are some weaknesses in the way that the data were collected. Facilities entered and left the system during the reporting period, and the number of facilities participating was substantially higher in the final year of the system than in the earlier years. This could introduce reporting bias, as facilities volunteering to participate, or to continue to participate for prolonged periods of time, may be significantly different than other facilities. They may, for example, be more invested in active infection prevention. However, Burton et al examined the trends in CLA-BSIs among facilities participating during the entire reporting period and noted a decline in infection rates due to all pathogens similar to that observed in the larger group, providing reasonable assurance that there wasn't systematic bias based on the population of reporting facilities. The overall rate of catheter usage in ICUs remained stable over that period. Further, the rate changes were consistent across medical, surgical, and combined medical-surgical units.
This is certainly good news for patient safety. However, the impressive numbers leave a very large unanswered question: What was the reason for this decline in CLA-BSIs? New CDC guidelines on prevention of CLA-BSIs were published in 2002,2 but this is unlikely to have had a dramatic effect for several reasons. First, the rates of infection due to methicillin-susceptible S. aureus and to all pathogens declined continuously starting in 1997. Although the reversal in the rise of the rate of MRSA CLA-BSIs was temporally associated with the guidelines, a cause-and-effect relationship is unlikely since the guidelines target infections generally, not one antibiotic resistant organism.
During the same period of the study, healthcare- and device-associated infections due to MRSA increased in the United States,3 suggesting that the declines in over-all CLA-BSIs and MRSA CLA-BSIs were independent of any MRSA control efforts.
The NNIS and NHSN data collection methodology isn't designed to answer the question. It would have been quite useful to have been able to identify any changes in practice that were associated with the decrease in infection rates. Changes in insertion techniques, catheter care, or catheter composition (i.e., antimicrobial coatings) are all potential contributors to improvements in the rates of CLA-BSIs. Unfortunately, surveillance data alone cannot provide us with any insight in that regard. Even though the data are very encouraging, it's frustrating to know the "what" without understanding the "why."