Expanding the Universe of Methicillin-Resistant Staphylococcus aureus Prevention

Staphylococcus aureus is one of the most common causes of infection in both the community and the health care setting. First described in 1961 (1), methicillin-resistant S. aureus (MRSA) has increased dramatically and now constitutes more than 50% of S. aureus isolates that cause infections in the hospital setting (24). Furthermore, MRSA infections are associated with poor clinical and economic outcomes (5). Asymptomatic colonization with MRSA often precedes clinical MRSA infection (6). Patients with MRSA colonization are typically identified only as a result of a positive clinical culture (that is, a culture obtained because of a suspected infection). However, the number of hospital patients asymptomatically colonized with MRSA far exceeds the number of patients identified through clinical cultures (7). Patients asymptomatically colonized with MRSA are a substantial reservoir for person-to-person spread in the hospital. Due in large part to a lack of rigorous scientific evidence, there remains no consensus on how best to limit transmission of this organism. Use of active surveillance cultures to identify and isolate patients asymptomatically colonized with MRSA has been recommended as one strategy (8, 9). However, exactly when and how these interventions should be implemented remains controversial (10). Past studies that evaluated the impact of active surveillance strategies were small, focused on only select hospital units or specific patient populations, or were limited to outbreaks. In light of the importance of MRSA and despite the uncertainty about how to contain it, external pressure for action increases. Legislation in several states mandates uniform surveillance for MRSA in health care settings. This one-size-fits-all legislative approach ignores the inherent differences in MRSA epidemiology among hospitals. These perhaps-precipitate actions seem to reflect the public's impatience with the health care professions' failure to act. The article by Robicsek and colleagues (11) in this issue describes the impact of a universal MRSA screening program. The authors conducted a multicenter, quasi-experimental study to test the effect of sequential surveillance interventions on hospital-associated MRSA infection. The primary outcome was the aggregate hospital-associated MRSA infection rate, defined as a combination of all MRSA bloodstream, respiratory, urinary tract, and surgical site infections occurring more than 48 hours after admission through day 30 after discharge. Rates were expressed as prevalence density of infections (that is, the number of infections per 10000 inpatient-days). In the 12-month baseline period, the hospitals did not do routine surveillance for MRSA colonization. In the first intervention period, which lasted 12 months, the hospitals did active surveillance for nasal MRSA colonization only in the intensive care unit (ICU) setting. They used polymerase chain reaction (PCR)based testing to decrease turnaround time. In the second intervention period, which lasted 21 months, the hospitals expanded PCR-based nasal surveillance to include all admitted patients. During all study periods, MRSA-colonized patients were placed on contact precautions, which consisted of a private room or sharing a room with another MRSA-colonized patient, gown and glove use for all persons entering the room, and dedicated room equipment. During the universal surveillance period, hospital units with low rates of screening received feedback aimed at improving adherence. The prevalence density of clinical hospital-associated MRSA infections decreased substantially during the universal surveillance period but not during the ICU-only surveillance period, compared with the baseline period. This study is an important contribution to the evidence about interventions against MRSA because it is the first to evaluate universal admission MRSA screening. The intervention was associated with an impressive, hospital-wide, 70% reduction in hospital-associated MRSA infections in less than 2 years. Could the results be explained by something other than the intervention? The MRSA infection rates were elevated but unchanged throughout the baseline period, which makes regression to the mean an unlikely alternative explanation. Adherence to handwashing and contact precautions reduce the transmission of resistant organisms yet are often suboptimal (12, 13). The ongoing feedback provided as part of the universal surveillance period might have increased adherence to these practices. However, better handwashing practices alone are unlikely to fully account for the large reduction in MRSA rates. The straightforward interpretation of the study resultsscreening for MRSA reduces MRSA infectionsis not necessarily correct because the hospitals implemented several co-interventions when they expanded surveillance to all admitted patients. In the universal surveillance period, the hospitals provided ongoing feedback to optimize adherence to screening. Furthermore, turnaround time of the PCR-based MRSA detection method was shorter during universal screening (0.67 day) than during ICU-only surveillance (2.5 days). The shorter the turnaround time, the quicker an MRSA-colonized patient is placed on contact precautions to decrease the likelihood of transmitting MRSA to others. Finally, treatment to reduce MRSA colonization was recommended only during the universal screening period. Although controversial, eradicating MRSA carriage may decrease the likelihood of subsequent clinical infection (14). These co-interventions do not raise concerns that the study overestimated the decrease in MRSA infections during universal screening. The remarkable decrease in MRSA infections coincident with universal MRSA surveillance may suggest that all hospitals adopt universal MRSA screening on admission. I believe this action would be premature. We need to know precisely which component(s) of the intervention was most important. Clarifying the role of decolonization with mupirocin (a topical antibiotic applied to the nasal passages) is important because its efficacy for long-term MRSA eradication is unknown and it may promote emergence of mupirocin resistance (15). In addition, we need to know the relative contribution of PCR-based MRSA detection methods because they are more expensive than traditional cultures (16). Finally, MRSA epidemiology and patient populations differ substantially across institutions and regions (4, 17). Each institution may need to tailor its intervention to its unique needs and resources. For example, specific patient populations, such as nursing home residents, may constitute a large proportion of all newly admitted patients colonized with MRSA at a given institution. Targeting these high-risk populations for screening may be the most cost-effective strategy (8). Prediction rules have been developed to inform a more efficient approach to MRSA admission screening (18). Universal MRSA screening will require considerable commitment and support from the hospital administration. Robsicek and colleagues estimated that universal screening was associated with 85 fewer MRSA infections in the 3 hospitals. Given the substantial economic impact of MRSA (5), a comprehensive universal screening program could be cost-effective (19). Demonstrating the economic value of infection control to hospital administrators is now a critical function of the hospital epidemiologist (20). This function takes on added economic importance in light of the Centers for Medicare & Medicaid Services' recent plans to eliminate additional reimbursement for certain hospital-acquired infections, as part of the Deficit Reduction Act of 2005. However, if hospital infection control resources shift primarily to MRSA screening, many other infection control activities may be severely curtailed. Somehow, hospitals must mobilize additional resources for new initiatives while maintaining existing infection control activities. The United Kingdom thinks expenditures on infection control are worthwhile. The U.K. Health Secretary recently announced government funding to enable each hospital trust in England to recruit 2 infection control nurses, 2 isolation nurses, and an antimicrobial pharmacist. Failure to act decisively to slow the continued emergence of MRSA has resulted largely from the lack of rigorous scientific evidence. More high-quality, cluster-randomized, controlled trials and quasi-experimental studies are critically needed to fully inform interventions designed to address MRSA. In particular, future work should investigate the efficacy and cost-effectiveness of specific components (for example, PCR-based detection, targeted versus universal surveillance, and decolonization) of intervention strategies. These research priorities have a broader relevance than simply controlling MRSA: Multidrug-resistant, gram-negative pathogens create great concern, given the few therapeutic options and lack of new drug development targeting these organisms. As with MRSA, we lack sufficiently rigorous scientific evidence about infection control interventions to prevent spread of these organisms. Recently, the U.S. Congress began deliberations on legislation to address some of these deficiencies; the Strategies to Address Antimicrobial Resistance (STAAR) Act seeks to strengthen federal antimicrobial resistance surveillance, prevention and control, and research efforts. Robsicek and colleagues identify unacceptably high MRSA infection rates as the motivation for their intervention. Few would argue that current MRSA rates are acceptable, and for many, the only acceptable rate of MRSA is no MRSA. This study is an important step toward that ultimate goal, but it is just 1 step. Unfortunately, the one-size-fits-all approach is probably not sensible for MRSA screening. As each institution continues to refine its own plan to address MRSA, we need better evidence to point us toward what works best in the compl