Increasing burden of methicillin-resistant Staphylococcus aureus hospitalizations at US academic medical centers, 2003-2008

Abstract

Objective: The incidence of invasive methicillin-resistant Staphylococcus aureus (MRSA) infections in the United States decreased during 2005-2008, but noninvasive community-associated MRSA (CA-MRSA) infections also frequently lead to hospitalization. We estimated the incidence of all MRSA infections among inpatients at US academic medical centers (AMCs) per 1,000 admissions during 2003-2008.

Design: Retrospective cohort study.

Setting and participants: Hospitalized patients at 90% of nonprofit US AMCs during 2003-2008.

Methods: Administrative data on MRSA infections from a hospital discharge database (University HealthSystem Consortium [UHC]) were adjusted for underreporting of the MRSA V09.0 International Classification of Diseases, Ninth Revision, Clinical Modification code and validated using chart reviews for patients with known MRSA infections in 2004-2005, 2006, and 2007.

Results: The mean sensitivity of administrative data for MRSA infections at the University of Chicago Medical Center in three 12-month periods during 2004-2007 was 59.1%. On the basis of estimates of billing data sensitivity from the literature and the University of Chicago Medical Center, the number of MRSA infections per 1,000 hospital discharges at US AMCs increased from 20.9 (range, 11.1-47.7) in 2003 to 41.7 (range, 21.9-94.0) in 2008. At the University of Chicago Medical Center, among infections cultured more than 3 days prior to hospital discharge, CA-MRSA infections were more likely to be captured in the UHC billing-derived data than were healthcare-associated MRSA infections.

Conclusions: The number of hospital admissions for any MRSA infection per 1,000 hospital admissions overall increased during 2003-2008. Use of unadjusted administrative hospital discharge data or surveillance for invasive disease far underestimates the number of MRSA infections among hospitalized patients.

FIGURE 1

Overlap of methicillin-resistant Staphylococcus aureus (MRSA) surveillance data from University of Chicago Medical Center (UCMC) surveillance and University HealthSystem Consortium (UHC) administrative data. A, From July 1, 2004, through June 30, 2005, of the 312 different inpatients identified through clinical microbiology laboratory surveillance who had MRSA infections, 139 were also identified by administrative (billing) data. Of the 252 hospitalized patients identified by administrative data as having an MRSA-related hospital stay, 113 were not identified by surveillance. All of these patients had medical records reviewed: 71 did not have MRSA infections, and 42 did have MRSA infections. The total number of patients with MRSA infections in 2004–2005, then, was 354 (ie, the sum of 173, 139, and 42). A similar analysis was performed for the calendar years 2006 (B) and 2007 (C).