title: Comorbidity risk-adjustment measures were developed and validated for studies of antibiotic-resistant infections.
abstract: OBJECTIVE
  Comorbidities are often included in risk-factor models for nosocomial antibiotic-resistant bacterial infections, and aggregate comorbidity measures are valuable because they allow one variable to represent many. This study aimed to develop new aggregate comorbidity measures based upon the Chronic Disease Score (CDS) for assessing the comorbidity-attributable risk of methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE) nosocomial infections.
  
  
  METHODS
  For each outcome, two retrospective cohort studies of hospitalized patients were conducted. Outcomes were a first MRSA or VRE positive clinical culture obtained 48 hours or more postadmission. Each cohort was divided into development (July 1998-2001) and validation (August 2001-2003) samples. New comorbidity measures were created for MRSA (CDS-MRSA), VRE (CDS-VRE), or any nosocomial infection outcome (CDS-ID) using logistic regression and subsequently validated. Model discrimination was measured using the c-statistic.
  
  
  RESULTS
  Discrimination of the CDS-MRSA (c=0.60), CDS-VRE (c=0.65), and CDS-ID (MRSA: c=0.57; VRE: c=0.64) was greater than that of the original CDS (MRSA: c=0.52; VRE: c=0.57).
  
  
  CONCLUSIONS
  The CDS-MRSA, CDS-VRE, and CDS-ID are new infectious disease specific comorbidity risk-adjustment measures that will be useful for the quality of future epidemiologic studies of MRSA, VRE, and other infectious diseases.
authors.affiliation: Department of Epidemiology and Preventive Medicine, University of Maryland, Baltimore, MD 21201, USA. jmcgrego@epi.umaryland.edu
authors.forename: Jessina C
authors.initials: JC
authors.lastname: McGregor
authors.forename: Eli N
authors.initials: EN
authors.lastname: Perencevich
authors.forename: Jon P
authors.initials: JP
authors.lastname: Furuno
authors.forename: Patricia
authors.initials: P
authors.lastname: Langenberg
authors.forename: Kathleen
authors.initials: K
authors.lastname: Flannery
authors.forename: Jingkun
authors.initials: J
authors.lastname: Zhu
authors.forename: Jeffrey C
authors.initials: JC
authors.lastname: Fink
authors.forename: Douglas D
authors.initials: DD
authors.lastname: Bradham
authors.forename: Anthony D
authors.initials: AD
authors.lastname: Harris
mesh_terms: D015897:Comorbidity; D003428:Cross Infection / Q000453:epidemiology*; D024881:Drug Resistance, Bacterial; D005260:Female; D016908:Gram-Positive Bacterial Infections / Q000453:epidemiology*; D006801:Humans; D008297:Male; D016106:Methicillin Resistance; D008875:Middle Aged; D015203:Reproducibility of Results; D012189:Retrospective Studies; D020379:Risk Adjustment / Q000379:methods; D012307:Risk Factors; D013203:Staphylococcal Infections / Q000453:epidemiology*; D020713:Vancomycin Resistance