Analysis of 1560 Inpatient and Outpatient Escherichia coli Isolates from across Canada—Results from the CANWARD 2007 Study
Authors: Lagacé-Wiens Philippe RS , DeCorby Mel , Baudry Patricia J , Hoban Daryl J , Karlowsky James A , The Canadian Antimicrobial Resistance Alliance (CARA)  , Zhanel George G 
Published: May 2016

OBJECTIVES: Escherichia coli was the most common pathogen isolated
in the Canadian Ward Surveillance Study (CANWARD 2007)
and remains one of the most common pathogens isolated in all health
care settings. An in‐depth analysis of all E coli isolates was performed
to determine the distribution and demographics associated with resistance
to antimicrobials, presence of extended‐spectrum beta‐lactamases
(ESBLs) and multidrug resistance (MDR; concurrent resistance to
agents from three or more different antimicrobial classes).
METHODS: The CANWARD 2007 study characterized pathogens
isolated from inpatient (surgical and medical wards, and intensive care
units) and outpatient (emergency departments and clinics) areas of
12 Canadian hospitals between January and December 2007. E coli
susceptibility to 12 antimicrobials was determined, ESBL production
was determined, and a multivariate nominal logistic regression model
was designed to determine if sex, isolation from a sterile site, inpatient
versus outpatient status, and age were significantly associated with
susceptibility to the tested antimicrobials, MDR or ESBL production.
RESULTS: In total, 1702 E coli isolates, representing 21.6% of all
isolates collected in the CANWARD 2007 study, were investigated.
Of these, 1560 isolates fell within the primary objective of the study
and were included in the present analysis. Susceptibilities were greater
than 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%), the
fluoroquinolones (ciprofloxacin, 79.4%; levofloxacin, 79.9%) and
trimethoprim‐sulfamethoxazole (75.7%) were less active agents. In
the multivariate model, invasive isolates were significantly associated
with lower susceptibility rates for trimethoprim‐sulfamethoxazole.
Increasing age was associated with lower susceptibility to fluoroquinolones,
ceftriaxone, cefepime, gentamicin and nitrofurantoin, as well as
ESBL production. Sex was not associated with resistance to any antimicrobial
or to ESBL production. Inpatient status was associated with
higher resistance rates to amoxicillin‐clavulanate, cefazolin, fluoroquinolones
and trimethoprim‐sulfamethoxazole. Isolation of an ESBL
producer was only found to be independently associated with age,
being more common in older patients. MDR was not found to be associated
with any variable measured when ESBL producers were
excluded from analysis.
CONCLUSIONS: E coli antimicrobial susceptibility varies according
to patient factors. Age and inpatient status were the most important
determinants in the present analysis and should be considered when
prescribing empirical antimicrobial therapy. Fluoroquinolones and
sulfonamides should be used cautiously and in consideration of local
resistance patterns for infections caused by E coli, due to lower susceptibility
rates. Independent factors associated with antimicrobial resistance
were age, inpatient status and isolation from a sterile site. These
factors should be considered when empirically treating infections
likely caused by E coli. Local antimicrobial prescribing practices, in
particular the liberal use of fluoroquinolones, and inadequate infection
control practices may be reducing susceptibility rates.