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Canadian Journal of Infectious Diseases and Medical Microbiology
Volume 26, Issue 1, Pages 33-38
Original Article

Value of an Aggregate Index in Describing The Impact of Trends in Antimicrobial Resistance for Escherichia coli

David M Patrick,1,2 Catharine Chambers,1 Dale Purych,3,4 Mei Chong,1 Diana George,1 and Fawziah Marra5

1British Columbia Centre for Disease Control, Canada
2School of Population and Public Health, University of British Columbia, Vancouver, Canada
3LifeLabs Medical Laboratory Services, Canada
4Fraser Health Authority, Surrey, British Columbia, Canada
5Faculty of Pharmaceutical Services, University of British Columbia, Vancouver, British Columbia, Canada

Copyright © 2015 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


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.