title: Value of an aggregate index in describing the impact of trends in antimicrobial resistance for Escherichia coli.
abstract: BACKGROUND
  Drug resistance indexes (DRIs) quantify the cumulative impact of antimicrobial resistance on the likelihood that a given pathogen will be susceptible to antimicrobial therapy.
  
  
  OBJECTIVE
  To derive a DRI for community urinary tract infections caused by Escherichia coli in British Columbia for the years 2007 to 2010, and to examine trends over time and across patient characteristics.
  
  
  METHODS
  Indication-specific utilization data were obtained from BC PharmaNet for outpatient antimicrobial prescriptions linked to diagnostic information from physician payment files. Resistance data for E coli urinary isolates were obtained from BC Biomedical Laboratories (now part of LifeLabs Medical Laboratory Services). DRIs were derived by multiplying the rate of resistance to a specific antimicrobial by the proportional rate of utilization for that drug class and aggregating across drug classes. Higher index values indicate more resistance.
  
  
  RESULTS
  Adaptive-use DRIs remained stable over time at approximately 18% (95% CI 17% to 18%) among adults ≥15 years of age and approximately 28% (95% CI 26% to 31%) among children <15 years of age. Similar results were observed when proportional drug use was restricted to the baseline year (ie, a static-use model). Trends according to age group suggest a U-shaped distribution, with the highest DRIs occurring among children <10 years of age and adults ≥65 years of age. Males had consistently higher DRIs than females for all age groups.
  
  
  CONCLUSIONS
  The stable trend in adaptive-use DRIs over time suggests that clinicians are adapting their prescribing practices for urinary tract infections to local resistance patterns. Results according to age group reveal a higher probability of resistance to initial therapy among young children and elderly individuals.
authors: British Columbia Centre for Disease Control; ; School of Population and Public Health, University of British Columbia, Vancouver;
authors: David M
authors: DM
authors: Patrick
authors: British Columbia Centre for Disease Control;
authors: Catharine
authors: C
authors: Chambers
authors: LifeLabs Medical Laboratory Services; ; Fraser Health Authority, Surrey;
authors: Dale
authors: D
authors: Purych
authors: British Columbia Centre for Disease Control;
authors: Mei
authors: M
authors: Chong
authors: British Columbia Centre for Disease Control;
authors: Diana
authors: D
authors: George
authors: Faculty of Pharmaceutical Services, University of British Columbia, Vancouver, British Columbia.
authors: Fawziah
authors: F
authors: Marra
keywords: Antimicrobial resistance; Drug resistance index; Escherichia coli