Declining MRSA Infections at a Tertiary Care Center: Exploration of Trends and Etiology

By William Ashford and Mary M. McFadden, RN, MHA, CIC, CHS

Editor's note: For graphs and charts, please refer to the May 2014 print edition of ICT.

Methicillinresistant S. aureus (MRSA) is a concern to all healthcare providers as MRSA infections are associated with significant patient morbidity and mortality. MRSA infected patients have nearly twice the mortality rate, longer hospital stays, and higher health costs than those with methicillinsusceptible S. aureus (MSSA) infections. The outcomes for patients surgically infected with MRSA are worse with mortality rates 3.4 times higher than patients surgically infected with MSSA.(1) MRSA colonized or infected patients readily contaminate their surroundings and healthcare personnel with whom they come in contact. Therefore, MRSA prevention in the hospital setting is a critical component of patient and provider safety.

The percentage of S. aureus infections in the U.S. classified as MRSA has been rising. In a retrospective study analyzing the prevalence of MRSA as a percentage of S. aureus infections in the United States, it was found that MRSA increased from 32.7 percent to 53.8 percent of isolated S. aureus strains from 1998 to 2007.(2) In a 2011 study, 59 percent of S. aureus isolates were found to be MRSA.(3) This suggests that the proportion of resistant strains of S. aureus continues to rise. While the increasing proportion of S. aureus identified as MRSA is concerning, examining actual infection rates with MRSA over time may better indicate the current status of our fight against MRSA.

Although the percentage of S. aureus infections identified as MRSA is growing, the overall incidence of MRSA infections may actually be falling. According to the CDC, national rates of hospital-acquired MRSA infections overall may have decreased during the period from 2005 to 2008 by 28 percent, and recent studies show this decline may have continued at least through 2011.(4-5) While more data on MRSA surveillance nationwide is needed to confirm the trend, it appears that MRSA infection rates are declining in the United States.

It is unclear if MRSA-specific preventions practices such as active screening and preemptive contact isolation of colonized patients can be solely credited for this apparent decrease in MRSA infections, as the decline began prior to widespread adoption of such interventions.(6) However, implementation and tighter adherence to general infection prevention practices could potentially explain the decline.(7)

With these issues in mind, we conducted a study to investigate a reduction in MRSA infection rates at our institution and used multiple parameters to analyze data collected by our infection prevention team. MedStar Georgetown University Hospital (MGUH) is an academic teaching facility with specialties including, among others, oncology, orthopedics, and transplant surgery. From mid 2008 to mid 20011, MGUH experienced a 32 percent decrease in MRSA infections. In the medical and surgical intensive care units, GUH experienced a decline of 76 percent and 82 percent respectively over the period of interest. The remainder of this article will describe our declining MRSA infection rates and the possible relationship of this decline to changes in infection prevention practices.

In a retrospective review of the MGUH infection prevention database, we examined rates of hospital and community associated MRSA and correlated changes in rates with ongoing infection prevention practices. We reviewed rates of MRSA infection over the past three years, and determined the source of infection as well as geographic location within the hospital.

Total MRSA infection rates at Georgetown University Hospital declined by 32 percent over the three-year period from mid-2008 to mid-2011. Healthcare-acquired MRSA infections (which account for 22 percent of total MRSA infections) dropped 37 percent and Georgetown’s five ICUs collectively experienced a 45 percent decline in MRSA infection rate over the same period. Perhaps MRSA’s most detrimental mode of infections, bloodstream infections, fell by 35 percent. 
    
Special attention was paid to units with the most MRSA infections, the medical intensive care unit (MICU) and surgical intensive care unit (SICU). Before 2010, preemptive isolation precautions were taken for every patient admitted to the MICU. Upon arrival, patients were placed on contact isolation until a culture of the anterior nares was negative for MRSA colonization. Because MICU infection rates did not appear to be significantly different from other units, this preemptive isolation precaution was discontinued in the MICU in May 2010. We did not expect to see a change in infection rates following this change in policy, and in fact, might have anticipated a slight increase in MRSA infections. However, the year after discontinuation of preemptive isolation precautions, the MICU experienced a 76 percent and 30 percent decline in total and healthcare-associated MRSA infections respectively. In the same time period, the SICU, which had never implemented such precautions, experienced a decline of 82 percent and 50 percent decline in total and healthcare-associated MRSA infections, respectively. In terms of infections per thousand patient days, the total MRSA infection rate in the MICU decreased from 3.4 in 2008-2009 to 0.81 in 2010-2011. The SICU experienced a drop from 2.9 in 2008-2009 to 0.52 in 2010-2011.

Although some literature supports preemptively isolating patients as a means to decrease MRSA infections, our experience calls this practice into question, as discontinuation was not associated with an increase in MRSA infections. In fact, fewer MRSA infections occurred after we stopped isolating preemptively. Additionally, the changes in MRSA infection rates in the MICU and SICU decreased by similar magnitudes, suggesting that the MICU’s practice of preemptively isolating patients had little influence.

In addition to the MRSA-specific practice of preemptive isolation, we also analyzed data concerning hand hygiene. Our data is based on observational recording of hand sanitization of health providers upon entering and exiting patient rooms. Average hand hygiene compliance in the MICU over the same time period as analyzed in the previous discussions rose 12 percent from 82 percent to 94 percent from mid-2008 to mid-2011. The surgical ICU’s average hand hygiene compliance over the same period increased 20 percent from 67 percent to 87 percent. 

General infection prevention practices such as observing standards for hand hygiene among healthcare providers have long been accepted as key to controlling hospital-acquired infections. Studies have shown dramatic reductions in infection rates even with modest compliance with hand hygiene standards.(8) The relationship between hand hygiene compliance and MRSA infection rates in the MICU and SICU at our institution reflects this, and it appears that the decline in MRSA infections correlates more closely with hand hygiene than the MRSA specific practice of preemptive isolation.

The declining rate of MRSA infections at MGUH appears to be consistent with national trends. A recent update on the national burden of MRSA shows significantly fewer overall MRSA infections in recent years.(9) While impossible to definitively declare the etiology of this decline, our study suggests an inverse correlation between MRSA infections and compliance of hospital staff with the general infection prevention practice of hand hygiene. Furthermore, our study indicates that MRSA-specific prevention practices such as active screening and isolation of colonized patients cannot be credited with decreasing infections. In fact, our study calls the effectiveness of such practices into question as the most precipitous drop in infections occurred following discontinuation of these precautions. While further investigation is needed to uncover the etiology of falling MRSA infection rates, it is clear that implementation of and adherence to general infection prevention practices will be critically important in the continuing struggle against drug-resistant organisms.

William Ashford is a fourth-year medical student at Georgetown University School of Medicine. H will graduate in May 2014 and will continue his training in orthopedic surgery at the Medical University of South Carolina.

Mary M. McFadden, RN, MHA, CIC, CHS, is the nurse epidemiologist and director of infection prevention at MedStar Georgetown University Hospital in Washington, D.C.  She is also a clinical advisor to the School of Medicine and to the MHSA students of Georgetown. 

References
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