Healthcare-related MRSA decreases, but reasons unclear

Aug 11, 2010 (CIDRAP News) – A new large-scale study of methicillin-resistant Staphylococcus aureus (MRSA) infections shows that infection rates have dropped in hospitalized people and those recently exposed to healthcare settings, but experts aren't sure what factors are driving the decline.

The findings, released today in the Journal of the American Medical Association (JAMA), are based on MRSA surveillance conducted by investigators with the US Centers for Disease Control and Prevention's (CDC's) Emerging Infections Program (EIP). To look for changes in infection rates, they analyzed all MRSA infections that occurred from 2005 through 2008 in the diverse geographic area covered by the EIP program, which includes nine metropolitan areas and covers a population of 15 million.

Previous studies have shown evidence of declining rates of MRSA infections related to healthcare settings in single or small collections of centers, but the new JAMA study with its large population confirms that the infections are declining.

Over the past few years, healthcare policy makers have put forward initiatives to curb healthcare-associated infections, with special efforts aimed at reducing those caused by MRSA. The study group's goal was to see if the rates of healthcare-associated MRSA infections have changed. It focused on invasive infections, those that occur in normally sterile body areas such as the bloodstream or joints.

Of the 21,503 MRSA infections the group identified during the surveillance period, 17,508 occurred in a hospital or in patients who had recently been in a healthcare setting. The investigators, led by the CDC's Alexander J. Kallen, MD, MPH, found that among hospitalized patients the rate of MRSA infections decreased 9.4% per year, and the rate for healthcare-associated community-onset MRSA infections decreased 5.7% each year.

Over the 4-year period, the hospital-acquired MRSA infections dropped 28% and the healthcare-associated community-onset infections dropped by 17%.

When the group singled out dialysis patients, who are at risk of developing central-line–related MRSA infections, they found the infection rate decreased by 19%, with most of the decrease occurring in 2008. The investigators said more research is needed to determine if that decrease persists.

Though study group members said they don't know what led to the decreased MRSA rates, they speculated that a number of factors may have contributed to the decline, such as the dissemination by the CDC and other groups of MRSA prevention practices in hospitals, particularly those aimed at preventing inpatient central-line infections.

They also wrote that shifting MRSA strains in healthcare settings could be a possible, but unlikely, contributor to the decrease.

Investigators concluded that their findings suggest the decrease in MRSA infections in US hospitals is real and could point to progress in preventing healthcare-associated MRSA. However, they said the main challenge will be increasing adherence to current infection control recommendations and preventing MRSA infections beyond healthcare settings.

In a related editorial in the same issue of JAMA, two infectious disease researchers from the University of Iowa Carver College of Medicine, Eli N. Perencevich, MD, MS, and Daniel J. Diekema, MD, wrote that the study's most important finding was that it documented a continuous decline in hospital-onset and healthcare-associated community-onset MRSA infections. They added that the decreases were even greater when the group limited its analysis to bloodstream infections and that the decreases were evident in dialysis patients.

Perencevich and Diekema wrote that it's not clear if MRSA-specific interventions explain the decreases, because the declines began in the United States and European Union before the control efforts were widely adopted. They also noted that many US hospitals have still not implemented MRSA control programs.

"Well-designed studies of factors that may have contributed to the decrease in MRSA should be performed to understand the reported decrease and direct additional control efforts," the two wrote.

Today's study serves as a reminder of how little experts know about the epidemiology of S aureus colonization and infection due to a lack of robust surveillance systems, they wrote. They added that the CDC's EIP model should be expanded to other populations and include surveillance of other important healthcare-associated pathogens.

"Robust surveillance programs that include collection of information about both host and pathogen will be required to begin to understand these issues," Perencevich and Diekema wrote.

In a statement today e-mailed to journalists, Society for Healthcare Epidemiology of America (SHEA) said that it was encouraged by the study findings, which serve as a reliable measure of strides that healthcare facilities have made in reducing healthcare-associated infection.

The group said that the data should be used to inform and sharpen the focus on implementing the best infection-prevention practices. "By increasing the rigor and level of research on the epidemiology of MRSA and other pathogens, we are able to better understand what works to prevent infections."

However, SHEA added that, though the study is promising, it does not reveal factors that led to the decline. The goal is more science-based interventions that stem from good research that lead to a better understanding of healthcare-associated infections, they added.

"This cycle can only continue and flourish with rapid translation of this evidence into action at every level within out healthcare institutions," they said in the statement. "The report by Kallen et all represents an integral first step in this cycle."

Kallen AJ, Mu Y, Bulens S, et al. Health care-associated invasive MRSA infections, 2005-2008. JAMA 2010 Aug 11;304(6):641-8 [Full text]

Perencevich EN, Diekema DJ. Decline in invasive MRSA infection: where to go from here? (Editorial) JAMA 2010 Aug 11;304(6):687-9 [Extract]

See also:

Aug 10 JAMA press release

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