The emergency department--an evolving epicenter for healthcare worker acquisition of methicillin-resistant Staphylococcus aureus?

From Rush University Medical Center and John H. Stroger, Jr., Hospital of Cook County, Chicago, Illinois. Received December 14, 2009; accepted December 15, 2009; electronically published April 28, 2010. Infect Control Hosp Epidemiol 2010; 31(6):581-583 2010 by The Society for Healthcare Epidemiology of America. All rights reserved. 0899-823X/2010/3106-0004$15.00. DOI: 10.1086/652529 The colonization dynamics of Staphylococcus aureus, including that of methicillin-resistant S. aureus (MRSA), has been examined in various patient populations—outpatients, inpatients, healthcare workers, and even families. Colonization with S. aureus in up to one-third of individuals is persistent, but patients more often are colonized intermittently or never. Understanding the dynamics of colonization is important, because colonization provides a resistance iceberg for MRSA and because colonization usually precedes infection. The nares are believed to be the predominant site of staphylococcal colonization, and infection control strategies have been developed on the basis of this tenet (eg, nasal surveillance to prompt cohorting or isolation of patients with MRSA nasal colonization). Recently, the colonization dynamics of MRSA has been called into question with the emergence of MRSA among distinct patient populations who lack preceding healthcare exposures—so-called community-associated MRSA (CAMRSA). Recognition of the CA-MRSA epidemic has led to questions regarding colonization patterns, venues for transmission, relationship to infection, and appropriate infection control measures. CA-MRSA infections have been observed among patients without concomitant nasal colonization, and although infections are often minor skin and soft-tissue infections (SSTIs), severe disease has also been reported. CAMRSA strains have spread in community settings but have also entered healthcare facilities; they are the most common cause of SSTIs in many ambulatory and emergency department settings in the United States. Rates of nasal colonization with MRSA in pediatric and adult populations, including patients who receive care in outpatient clinics, hemodialysis centers, emergency departments, hospital wards, and intensive care units, vary by group and location. The importance of the healthcare worker as a link in this epidemiological chain is unclear. MRSA infections among patients that were linked to a colonized and/or infected healthcare worker have been described, with resolution of the outbreak occurring after implementation of increased infection control practices. However, in a recent review by Vonberg et al, asymptomatic healthcare workers were the likely source of MRSA in only 3 (1.6%) of 191 nosocomial MRSA outbreaks; most cases of transmission occurred among infected healthcare personnel. Recent studies have evaluated the prevalence of MRSA nasal colonization among asymptomatic healthcare workers in nonoutbreak settings. Two investigations of healthcare personnel in emergency departments revealed a prevalence of nasal MRSA carriage of 4.3% in a multicenter study and of 15% in a single-center study. This colonization prevalence is higher than that in the general US population. Gorwitz et al found that the prevalence of MRSA colonization among the general population increased from 0.8% to 1.5% from 2001–2002 to 2003–2004. It is unclear why the observed MRSA colonization prevalence in healthcare workers, in particular in emergency departments, appears disproportionately high compared with that of the general population. Perhaps exposure to wounds, a contaminated environment, or high levels of patient contact contribute to this discrepancy. The study by Elie-Turenne et al in this issue further assesses the prevalence of S. aureus and MRSA nasal colonization among various types of presumably asymptomatic healthcare workers in 3 different nonepidemic healthcare settings—intensive care unit, emergency department, and prehospital services. The overall MRSA nasal colonization prevalence among healthcare workers was 6.6%, once again a higher prevalence than in the general population. Whereas the prevalence of S. aureus nasal colonization was highest among paramedics (ie, in prehospital settings), nurses and therapists had the highest prevalence of MRSA nasal colonization. Furthermore, in comparison with the intensive care unit and prehospital services, the emergency department was the study setting with the greatest number of MRSA-positive