Methicillin-Resistant Staphylococcus aureus and Vancomycin-Resistant Enterococci Co-Colonization

Jon P. Furuno; Eli N. Perencevich; Judith A. Johnson; Marc-Oliver Wright; Jessina C. McGregor; J. Glenn Morris Jr; Sandra M. Strauss; Mary-Claire Roghman; Lucia L. Nemoy; Harold C. Standiford; Joan N. Hebden; Anthony D. Harris


Emerging Infectious Diseases. 2005;11(10) 

In This Article

Abstract and Introduction

We assessed the prevalence, risk factors, and clinical outcomes of patients co-colonized with vancomycin-resistant enterococci (VRE) and methicillin-resistant Staphylococcus aureus (MRSA) upon admission to the medical and surgical intensive care units (ICUs) of a tertiary-care facility between January 1, 2002, and December 31, 2003. Co-colonization was defined as a VRE-positive perirectal surveillance culture with an MRSA-positive anterior nares surveillance culture collected concurrently. Among 2, 440 patients, 65 (2.7%) were co-colonized. Independent risk factors included age (odds ratio [OR] 1.03, 95% confidence interval [CI] 1.01-1.05), admission to the medical ICU (OR 4.38, 95% CI 2.46-7.81), male sex (OR 1.93, 95% CI 1.14-3.30), and receiving antimicrobial drugs on a previous admission within 1 year (OR 3.06, 95% CI 1.85-5.07). None of the co-colonized patients would have been identified with clinical cultures alone. We report a high prevalence of VRE/MRSA co-colonization upon admission to ICUs at a tertiary-care hospital.

Methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE) cause nosocomial infections and are associated with increased rates of illness and death.[1,2] Both organisms are now endemic in many healthcare institutions, particularly in intensive care units (ICUs).[3] Vancomycin is commonly used to treat infections caused by MRSA; however, recent emergence of S. aureus infections with high-level resistance to vancomycin call into question the future effectiveness of vancomycin for these nosocomial infections.[4] All known vancomycin-resistant S. aureus (VRSA) isolates reported thus far have possessed the vanA gene, which confers resistance to vancomycin and is believed to have been acquired when an MRSA isolate conjugated with a co-colonizing VRE isolate.[5,6,7,8,9,10] Thus, patients simultaneously co-colonized with MRSA and VRE are likely at increased risk for colonization or infection by VRSA.

Patients in the ICU and other critically ill patients are at high risk for co-colonization with MRSA and VRE And, possibly, VRSA, since both organisms are endemic and associated with increased illness severity.[11,12] Despite the high risk, epidemiologic risk factors associated with co-colonization by MRSA and VRE in patients admitted to ICUs have not been described. In addition, previous studies in this population have been limited by the use of clinical cultures as markers for colonization, which underestimate the true proportion of patients colonized with these resistant organisms.[13,14,15]

To our knowledge, this study is the first to assess independent risk factors and outcomes for patients co-colonized with VRE and MRSA. The aim of this study was to estimate the prevalence, risk factors, and clinical outcomes of patients who are co-colonized by VRE and MRSA upon admission to the medical and surgical ICUs of a tertiary-care facility.


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