Analysis of 1560 Inpatient and OutpatientEscherichia coliIsolates from across Canada—Results from the CANWARD 2007 Study

OBJECTIVES: Escherichia coli was the most common pathogen isolatedin the Canadian Ward Surveillance Study (CANWARD 2007)and remains one of the most common pathogens isolated in all healthcare settings. An in-depth analysis of all E coli isolates was performedto determine the distribution and demographics associated with resistanceto antimicrobials, presence of extended-spectrum beta-lactamases(ESBLs) and multidrug resistance (MDR; concurrent resistance toagents from three or more different antimicrobial classes).METHODS: The CANWARD 2007 study characterized pathogensisolated from inpatient (surgical and medical wards, and intensive careunits) and outpatient (emergency departments and clinics) areas of12 Canadian hospitals between January and December 2007. E colisusceptibility to 12 antimicrobials was determined, ESBL productionwas determined, and a multivariate nominal logistic regression modelwas designed to determine if sex, isolation from a sterile site, inpatientversus outpatient status, and age were significantly associated withsusceptibility to the tested antimicrobials, MDR or ESBL production.RESULTS: In total, 1702 E coli isolates, representing 21.6% of allisolates collected in the CANWARD 2007 study, were investigated.Of these, 1560 isolates fell within the primary objective of the studyand were included in the present analysis. Susceptibilities were greaterthan 90% for meropenem (100%), ertapenem (100%), tigecycline(99.9%), piperacillin-tazobactam (97.9%), cefepime (97.9%), ceftriaxone(95.4%), nitrofurantoin (95.2%), cefoxitin (94.8%), amoxicillinclavulanate(92.9%) and gentamicin (91.4%). Cefazolin (89.4%), thefluoroquinolones (ciprofloxacin, 79.4%; levofloxacin, 79.9%) andtrimethoprim-sulfamethoxazole (75.7%) were less active agents. Inthe multivariate model, invasive isolates were significantly associatedwith lower susceptibility rates for trimethoprim-sulfamethoxazole.Increasing age was associated with lower susceptibility to fluoroquinolones,ceftriaxone, cefepime, gentamicin and nitrofurantoin, as well asESBL production. Sex was not associated with resistance to any antimicrobialor to ESBL production. Inpatient status was associated withhigher resistance rates to amoxicillin-clavulanate, cefazolin, fluoroquinolonesand trimethoprim-sulfamethoxazole. Isolation of an ESBLproducer was only found to be independently associated with age,being more common in older patients. MDR was not found to be associatedwith any variable measured when ESBL producers wereexcluded from analysis.CONCLUSIONS: E coli antimicrobial susceptibility varies accordingto patient factors. Age and inpatient status were the most importantdeterminants in the present analysis and should be considered whenprescribing empirical antimicrobial therapy. Fluoroquinolones andsulfonamides should be used cautiously and in consideration of localresistance patterns for infections caused by E coli, due to lower susceptibilityrates. Independent factors associated with antimicrobial resistancewere age, inpatient status and isolation from a sterile site. Thesefactors should be considered when empirically treating infectionslikely caused by E coli. Local antimicrobial prescribing practices, inparticular the liberal use of fluoroquinolones, and inadequate infectioncontrol practices may be reducing susceptibility rates