Another Success Story for Horizontal Infection Control Strategies—Which One?

Infections due to methicillin-resistant Staphylococcus aureus (MRSA) are associated with increased length of stay, cost, and mortality^{1, 2}. This is of particular importance in intensive care units (ICUs) where the burden of hospital-associated MRSA infections can be high³. Various infection control strategies have been put forth, particularly in ICUs, in an effort to reduce MRSA transmission and infection⁴. These strategies have included both vertical (i.e., pathogen specific) and horizontal (i.e., not-pathogen specific) approaches. Supporters of horizontal infection control approaches highlight the broader impact these interventions can have, particularly important now with increasing rates of multi-drug resistant gram-negative organisms⁵.

A recent cluster-randomized multicenter study by Huang, et al.⁶ examined the incremental benefits of active surveillance for MRSA colonization, decolonization, and daily chlorhexidine gluconate (CHG) bathing for reducing infections in ICUs. They compared three strategies: (1) nasal surveillance for detection of MRSA colonization and subsequent isolation of MRSA carriers, (2) surveillance and isolation of MRSA carriers with targeted decolonization of carriers with a 5 day regimen of intranasal mupirocin and CHG bathing, and (3) no screening for MRSA but universal decolonization with a 5 day regimen of mupirocin and daily CHG bathing for the duration of the ICU stay. They observed that universal decolonization (vertical and horizontal approach) was the most effective strategy for decreasing the rates of MRSA clinical isolates and bloodstream infections (BSIs) from any pathogen.

In this issue of Critical Care Medicine, Traa and colleagues⁷ performed a quasi-experimental study in a surgical ICU to determine the impact of various horizontal infection control strategies on the incidence of hospital-associated MRSA infections from 2005-2012. No active surveillance for MRSA colonization was performed during the study period. Several overlapping interventions were introduced: a hand hygiene program; oral chlorhexidine rinses for mechanically ventilated patients which was later augmented to a more comprehensive oral hygiene program; a multi-component central line associated bloodstream infection program which included application of 2% chlorhexidine gel dressings to line sites; daily CHG bathing; daily goal sheets; and use of chlorhexidine sulfadiazine coated central venous catheters. In addition, the authors note that since 2010 the practice of obtaining blood cultures from catheters was strongly discouraged. In the face of all these changes and interventions, the authors observed a significant decline in the incidence of MRSA infections from 2005 to 2012 as well as zero hospital-associated MRSA BSIs during the last five years of the study (2008-2012).

The study by Traa and colleagues⁷ is notable in that it demonstrates that it is feasible to have significant reductions in hospital-associated MRSA infections over a several year period solely using horizontal infection control strategies. In addition, in contrast to the work of Huang, et al.⁶, mupirocin was not used for decolonization yet a significant decline was observed, suggesting that bundled infection control approaches incorporating daily CHG bathing for decolonization may be sufficient. Given the concerns with development of mupirocin resistance if widespread use were adopted⁸, a successful infection control bundle without mupirocin may be desirable.

The current study⁷ also adds to the growing literature documenting the success of daily CHG bathing for reducing healthcare-associated infections (HAIs)^{6, 9-11}. Daily CHG bathing decreases the burden of patient skin contamination which can help prevent infections due to potential pathogens on patient skin. In addition, CHG bathing reduces the opportunity for contamination of healthcare worker hands and for contamination of the hospital environment, thereby decreasing cross-transmission of pathogens to other patients¹². As a horizontal infection control approach, regular CHG bathing has the added benefit of reducing HAIs due to a variety of pathogens and not just MRSA^{9, 11}. While reports of reduced susceptibility to CHG have so far been rare¹³, continued monitoring for this is essential as more hospitals institute daily CHG bathing of ICU patients.

A potential weakness of the study by Traa and colleagues⁷ is that we do not know which of the several overlapping interventions—if any—was most important for reducing MRSA infections and BSIs. In addition, aside from the hand hygiene program, we do not know what the compliance was for each of the various components, making it challenging to know which infection control measure should be recommended to attain the dramatic results they observed. The authors instituted a refresher hand hygiene campaign several years into the study, suggesting that compliance with certain strategies may have been variable and that frequent monitoring and reinforcement may be needed to ensure the success of certain infection control measures.

An additional limitation of the study is the lack of control variables (e.g., the incidence of MRSA infectious outside the surgical ICU), which have been previously reported to increase the scientific rigor of quasi-experimental studies¹⁴. The authors report that other ICUs at their hospital also observed a decrease in the incidence of MRSA infections, presumably due to implementation of infection control strategies in these other units. Including internal control variables would have strengthened the argument that the observed declines in the incidence of MRSA infections in the surgical ICU were attributable to the outlined interventions. Finally, it would have been valuable to know if the surgical ICU observed reductions in the incidence of infections due to pathogens other than MRSA, supporting the broader impact of horizontal infection control approaches.

Nonetheless, despite these limitations zero MRSA BSIs for 5 years is impressive. Other national studies have similarly observed declines in hospital-associated MRSA infections since 2005^{15, 16}. These national trends have in part been attributed to improved recognition of HAIs as well as implementation in ICUs across the country of various interventions such as those included in the current study¹⁵. As Traa and colleagues⁷ suggest, a cost-benefit analysis would be of value to inform future implementation of multi-component infection control interventions.

This study adds to the literature as it documents the ability to significantly decrease hospital-associated MRSA infections, including BSIs, without the use of active surveillance cultures. By implementing several horizontal infection control strategies—interventions that target pathogens beyond MRSA—the surgical ICU had five years of zero hospital-associated MRSA BSIs. This study also suggests that intranasal mupirocin may not be a necessary component of an infection control program aimed at reducing HAIs due to MRSA. The major take home message of the study by Traa and colleagues⁷ is that reductions in HAIs are possible, with perseverance and vigilance. While this study should be viewed in light of the mentioned limitations, zero MRSA BSIs are still zero MRSA BSIs.