• Heather J Adam, Melanie R Baxter, Ross J Davidson, Ethan Rubinstein, Sergio Fanella, James A Karlowsky, Philippe R S Lagacé-Wiens, Daryl J Hoban, George G Zhanel, and Canadian Antimicrobial Resistance Alliance (CARA).
• Department of Clinical Microbiology, Health Sciences Centre/Diagnostic Services of Manitoba, Winnipeg, Manitoba, Canada R3A 1R9. hadam@dsmanitoba.ca
• J. Antimicrob. Chemother. 2013 May 1; 68 Suppl 1: i31-7.

ObjectivesThe purpose of this study was to describe the association between age groups and antimicrobial resistance in the most commonly identified pathogens in Canadian hospitals.MethodsBetween 2007 and 2011, 27,123 clinically significant isolates, comprising 3580 isolates from children ≤ 18 years old, 12,119 isolates from adults 19-64 years old and 11,424 isolates from elderly patients aged ≥ 65 years old, were collected as part of the CANWARD surveillance study from tertiary-care centres across Canada. Antimicrobial susceptibility testing was performed according to CLSI guidelines. A multifactorial logistic regression model was used to determine the impact of demographic factors, including age groups, on antimicrobial resistance.ResultsStaphylococcus aureus, Escherichia coli, Streptococcus pneumoniae and Pseudomonas aeruginosa were in the top five organisms for all of the age groups. The proportions of S. aureus that were methicillin resistant, enterococci that were vancomycin resistant and E. coli that produced extended-spectrum β-lactamases were 11.2%, 0.7% and 1.0% for children, 22.8%, 4.6% and 4.3% for adults, and 28.0%, 3.8% and 4.9% for the elderly, respectively. Notable age-related differences in antimicrobial resistance patterns included the following: significantly less methicillin, clindamycin, clarithromycin and trimethoprim/sulfamethoxazole resistance in S. aureus from children; for E. coli, higher cefazolin and ciprofloxacin resistance in the elderly and less ceftriaxone, ciprofloxacin and gentamicin resistance in isolates from children; more S. pneumoniae isolates with penicillin MICs >1 mg/L in children; and for P. aeruginosa, higher resistance rates for meropenem, ciprofloxacin and levofloxacin in adults.ConclusionsThe assessment of antimicrobial susceptibility patterns by age group revealed that resistance rates are often higher in the older age groups; however, considerable variability in age-specific resistance trends for different pathogen-antimicrobial combinations was noted.

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