Replacement of HA-MRSA by CA-MRSA infections at an academic medical center in the midwestern United States, 2004-5 to 2008.

Michael Z David,Adriana Cadilla,Susan Boyle-Vavra,Robert S Daum,Herminia De Lencastre

doi:10.1371/journal.pone.0092760

Abstract

We noted anecdotally that infections designated as health care-associated (HA-) MRSA by epidemiologic criteria seemed to be decreasing in incidence at the University of Chicago Medical Center (UCMC) after 2004. We compared MRSA patients seen at any site of clinical care at UCMC and the isolates that caused their infections in 2004-5 (n = 545) with those in 2008 (n = 135). The percent of patients with MRSA infections cultured > 2 days after hospital admission decreased from 19.5% in 2004-5 to 7.4% in 2008 (p = 0.001). The percent in 2004-5 compared with 2008 who had a hospitalization (49.1% to 26.7%, p = 0.001) or surgery (43.0% to 14.1%, p<0.001) in the previous year decreased. In 2008 a greater percent of patients was seen in the emergency department (23.1% vs. 39.3%) and a smaller percent both in intensive care units (15.6% vs. 6.7%) and in other inpatient units (40.7% vs. 32.6%) (p<0.001). The percent of patients with CA-MRSA infections by the CDC epidemiologic criteria increased from 36.5% in 2004-5 to 62.2% in 2008 (p<0.001). The percent of MRSA isolates sharing genetic characteristics of USA100 decreased from 27.9% (152/545) to 12.6% (17/135), while the percent with CA-MRSA (USA300) characteristics increased from 53.2% (290/545) to 66.7% (90/135). The percent of infections that were invasive did not change significantly. Our data suggest that HA-MRSA infections, both by epidemiologic and microbiologic criteria, relative to CA-MRSA, decreased between 2004-5 and 2008 at UCMC.

Highlights

The epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) changed dramatically in the first decade of the twentyfirst century with the emergence of genotypically novel community-associated (CA-) MRSA strains [1]
We noted anecdotally that infections designated as health careassociated (HA-) MRSA by epidemiologic criteria seemed to be decreasing in incidence at the University of Chicago Medical Center (UCMC) after 2004
We found that CA-MRSA infections, whether defined by epidemiologic or microbiologic criteria, were very common among inpatients and outpatients in the clinic and the emergency departments (EDs) among both adults and children

Summary

Introduction

The epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) changed dramatically in the first decade of the twentyfirst century with the emergence of genotypically novel community-associated (CA-) MRSA strains [1]. CA-MRSA strains were first noted in the late 1990s as causes of skin and soft tissue infections (SSTIs) as well as severe invasive syndromes in people with no known previous exposure to a health care setting. The overall number of MRSA infections has increased [6] This has resulted from 4 epidemiologic trends. The incidence of outpatient and ED MRSA SSTIs [7,8] and the incidence of CA-MRSA infections resulting in hospitalization [9] has increased in the past decade. Fourth, during the past decade, among all MRSA infections in several U.S populations, there has been an increase in the percent that are classified epidemiologically as CA-MRSA [5,12,13,14]

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Results

Conclusion