Molecular characterization of methicillin-resistant Staphylococcus aureus (MRSA) nasal colonization and infection isolates in a Veterans Affairs hospital.

Kalyani E Eko,Brett M Forshey,Eli N Perencevich,Marin L Schweizer,Tara C Smith,Margaret Carrel

doi:10.1186/s13756-015-0048-5

Abstract

BackgroundNasal colonization with methicillin-resistant Staphylococcus aureus (MRSA) is associated with increased infection risk, yet colonization and infection isolates are rarely compared within the same study. The objectives of this study were to compare colonization and infection isolates from a Veterans Administration hospital in Iowa, and to determine the prevalence of livestock-associated MRSA (LA-MRSA) colonization and infection in a state with high livestock density.MethodsAll patients with available MRSA isolates collected through routine nasal screening (73%; n = 397) and from infections (27%; n = 148) between December 2010 and August 2012 were included and tested for spa type and presence of PVL and mecA genes. Clinical isolates were tested for antibiotic resistance patterns. Paired colonization and infection isolates were compared for genetic and phenotypic congruity.ResultsThe most common spa types were t002 (and other CC5-associated strains; 65%) and t008 (and other CC8-associated strains; 20%). No classic LA-MRSA spa types were identified. CC5-associated strains were less likely to be associated with infections (22%; 77/353) compared with CC8-associated strains (49%; 53/109). MRSA colonization was more common among patients with infections (71%) compared with the general screening population (7%). In most cases (82%; 28/34), paired colonization and infection isolates were genetically and phenotypically indistinguishable.ConclusionsOur data demonstrate a direct link between antecedent nasal colonization and subsequent MRSA infection. Further, our data indicate variability in colonization and infection efficiency among MRSA genotypes, which points to the need to define the molecular determinants underlying emergence of S. aureus strains in the community and nosocomial setting.

Highlights

As the leading cause of multi-drug resistant nosocomial infections in the U.S [1], methicillin-resistant Staphylococcus aureus (MRSA) is often responsible for ventilatorassociated pneumonia, septicemia associated with venousMRSA colonization is associated with increased risk for MRSA infection [5], with an estimated 4-fold increase inEko et al Antimicrobial Resistance and Infection Control (2015) 4:10 the odds of infection [6]
The majority of samples (397/545; 72.8%) were collected through routine nasal screening for MRSA colonization upon hospital admission, while the rest (148; 27.2%) were collected from infections
Our results support previous studies [4,25,26,27] that demonstrate a link between nasal colonization and subsequent clinical infections with MRSA, as colonization upon hospital admission was much higher among patients with MRSA infections than in the general Veterans Affairs (VA) patient population

Summary

Introduction

As the leading cause of multi-drug resistant nosocomial infections in the U.S [1], methicillin-resistant Staphylococcus aureus (MRSA) is often responsible for ventilatorassociated pneumonia, septicemia associated with venousMRSA colonization is associated with increased risk for MRSA infection [5], with an estimated 4-fold increase inEko et al Antimicrobial Resistance and Infection Control (2015) 4:10 the odds of infection [6]. Residents often live in close proximately to large scale livestock production facilities, such as confined animal feeding operations (CAFOs), where LA-MRSA and other MRSA strains have been found to colonize swine [8,9]. Our previous study found that geographic proximity to large swine populations was associated with increased risk of MRSA colonization among VA patients in Iowa [10]. Nasal colonization with methicillin-resistant Staphylococcus aureus (MRSA) is associated with increased infection risk, yet colonization and infection isolates are rarely compared within the same study. The objectives of this study were to compare colonization and infection isolates from a Veterans Administration hospital in Iowa, and to determine the prevalence of livestock-associated MRSA (LA-MRSA) colonization and infection in a state with high livestock density

Objectives

Methods

Results

Discussion

Conclusion