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Canadian Journal of Infectious Diseases and Medical Microbiology
Volume 20 (2009), Suppl A, Pages 37A-42A
http://dx.doi.org/10.1155/2009/286823
CANWARD 2007

Antimicrobial-Resistant Streptococcus pneumoniae in Canadian Hospitals: Results from the 2007 CANWARD Study

Aleksandra K Wierzbowski,1 Franil Tailor,1 Kim Nichol,2 James A Karlowsky,1,2 Daryl J Hoban,1,2 and George G Zhanel1

1University of Manitoba, Department of Medical Microbiology, Manitoba, Canada
2Health Sciences Centre, Winnipeg, Manitoba, Canada

Copyright © 2009 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.

Abstract

BACKGROUND: The Canadian Ward Surveillance Study (CANWARD 2007) tested isolates collected from January to December 2007 from 12 Canadian hospitals to a range of antimicrobial agents. The present paper focuses on antimicrobial resistance in Streptococcus pneumoniae in Canadian hospitals, with an emphasis on macrolide resistance. MEtHODS: Minimum inhibitory concentrations of antimicrobial agents were determined using the broth microdilution method and interpreted according to Clinical and Laboratory Standards Institute breakpoints. Macrolide-nonsusceptible strains (clarithromycin minimum inhibitory concentrations 0.5 μg/mL or greater) were analyzed by multiplex polymerase chain reaction for the presence of mefA and ermB genes. RESULTS: S pneumoniae represented 9.0% (706 of 7881) of all isolates collected in CANWARD 2007. Of the 706 S pneumoniae isolates collected, 33.1% (234) were from blood and 66.9% (472) were from respiratory specimens. The overall resistance (resistant and intermediate) rates for S pneumoniae isolated from respiratory and blood specimens, respectively, were: penicillin (23.9%, 14.4%), clarithromycin (22.1%, 12.6%), trimethoprim-sulfamethoxazole (14.7%, 11.5%), doxycycline (7.8%, 5.1%) and clindamycin (7.1%, 3.3%). Multidrug resistance (resistance to penicillin, clarithromycin and trimethoprimsulfamethoxazole) accounted for 2% (n=9) and 0.5% (n=1) of respiratory and blood isolates, respectively. Susceptibility of 95% or greater was found with amoxicillin-clavulanic acid (99.5%, 99.3%), ceftriaxone (99.5%, 100%), cefuroxime (95.0%, 96.8%), ertapenem (99.8%, 100%), meropenem (96.1%, 99.5%) and levofloxacin (99.1%, 100%) for respiratory and blood specimens, respectively. No resistance to vancomycin, tigecycline, cethromycin or telithromycin was found. mefA was present in 53.6% (52 of 97) of respiratory and 59.3% (16 of 27) of blood macrolide-nonsusceptible S pneumoniae, while ermB was present in 38.1% (37 of 97) of respiratory and 37% (10 of 27) of blood isolates. Eight of 97 (8.2%) respiratory and one of 27 (3.7%) blood isolates contained both mefA and ermB genes. CONCLUSIONS: S pneumoniae is a common organism isolated from clinical specimens in Canadian hospitals. Resistance was highest to penicillin and clarithromycin, while ceftriaxone and levofloxacin susceptibility were both greater than 99%. No isolates resistant to vancomycin, tigecycline, linezolid or the ketolides were found. Resistance rates were higher among respiratory tract isolates of S pneumoniae than among blood isolates. Macrolide efflux, mefA, was the predominant mechanism of macrolide resistance among both respiratory and blood clarithromycin-nonsusceptible isolates.