Change of Antibiotic Susceptibility Testing Guidelines from CLSI to EUCAST: Influence on Cumulative Hospital Antibiograms
et al. (2013) Change of Antibiotic Susceptibility Testing Guidelines from CLSI to
EUCAST: Influence on Cumulative Hospital Antibiograms . PLoS ONE 8(11): e79130. doi:10.1371/journal.pone.0079130
Change of Antibiotic Susceptibility Testing Guidelines from CLSI to EUCAST: Influence on Cumulative Hospital Antibiograms
Aline Wolfensberger 0 1
Hugo Sax 0 1
Rainer Weber 0 1
Reinhard Zbinden 0 1
Stefan P. Kuster 0 1
Michael 0 1
Vishnu Chaturvedi, California Department of Public Health, United States of America
0 the Clinical and Laboratory Standards Institute (CLSI) 2009
1 1 Division of Infectious Diseases and Hospital Epidemiology, University Hospital and University of Zurich , Zurich , Switzerland , 2 Institute of Medical Microbiology, University of Zurich , Zurich , Switzerland
Objective: We studied whether the change in antibiotic susceptibility testing (AST) guidelines from CLSI to EUCAST influenced cumulative antibiograms in a tertiary care hospital in Switzerland. Methods: Antibiotic susceptibilities of non-duplicate isolates collected within a one-year period before (period A) and after (period B) changing AST interpretation from CLSI 2009 to EUCAST 1.3 (2011) guidelines were analysed. In addition, period B isolates were reinterpreted according to the CLSI 2009, CLSI 2013 and EUCAST 3.1 (2013) guidelines. Results: The majority of species/drug combinations showed no differences in susceptibility rates comparing periods A and B. However, in some gram-negative bacilli, decreased susceptibility rates were observed when comparing CLSI 2009 with EUCAST 1.3 within period B: Escherichia coli / cefepime, 95.8% (CLSI 2009) vs. 93.1% (EUCAST 1.3), P=0.005; Enterobacter cloacae / cefepime, 97.0 (CLSI 2009) vs. 90.5% (EUCAST 1.3), P=0.012; Pseudomonas aeruginosa / meropenem, 88.1% (CLSI 2009) vs. 78.3% (EUCAST 1.3), P=0.002. These differences were still evident when comparing susceptibility rates according to the CLSI 2013 guideline with EUCAST 3.1 guideline. For P. aeruginosa and imipenem, a trend towards a lower antibiotic susceptibility rate in ICUs compared to general wards turned into a significant difference after the change to EUCAST: 87.9% vs. 79.8%, P=0.08 (CLSI 2009) and 86.3% vs. 76.8%, P=0.048 (EUCAST 1.3). Conclusions: The change of AST guidelines from CLSI to EUCAST led to a clinically relevant decrease of susceptibility rates in cumulative antibiograms for defined species/drug combinations, particularly in those with considerable differences in clinical susceptibility breakpoints between the two guidelines.
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These authors contributed equally to this work.
The European Committee for Antimicrobial Susceptibility
Testing (EUCAST) was initiated to harmonize
inhibitory concentration (MIC) breakpoints across Europe [1]. In
line with many European clinical laboratories, the University of
changed its antibiotic susceptibility testing (AST) system from
methodology to the EUCAST 1.3 AST guidelines on 1st July
In general, EUCAST recommends lower resistance MIC
breakpoints than CLSI, in particular for Gram-negative bacteria,
and, in part, abandoned the intermediate susceptibility zone.
These changes have been shown to result in different
susceptibility rates, e.g. higher cefepime and meropenem
resistance rates in Pseudomonas aeruginosa [4], higher
ceftazidime and ceftriaxone resistance rates in Escherichia coli
causing bacteremia [5], higher ceftazidime resistance in
ESBLproducing E. coli and Klebsiella pneumonia [6], and higher
cefepime and ceftazidime resistance in ESBL producing E. coli
[7]. However, the actual effect of the guideline changes on
cumulative hospital antibiograms is unknown, even though
local cumulative antibiograms are important for guiding
empirical antibiotic therapy [8,9], and changes in cumulative
resistance rates may influence the choice of empirical
antimicrobial treatment [10].
This study was designed to determine whether and to which
extent susceptibility rates in cumulative antibiograms of the five
most prevalent bacterial species in our tertiary-care hospital
would differ between two consecutive years before and after
changing from CLSI 2009 to EUCAST 1.3 (2011) AST
guidelines. Furthermore, we determined whether differences in
cumulative antibiograms represented true changes in
antimicrobial susceptibility, or if they were merely an effect of
guideline changes.
In addition, as resistance rates of cumulative antibiograms
from general ward specimens reportedly differ from those
found on intensive care units (ICUs), we aimed to determine
whether guideline dependent changes differed between ICUs
and general wards [11,12].
Materials and Methods
Setting
The University Hospital Zurich, Zurich, Switzerland, is an 871
bed tertiary-care teaching hospital covering all medical
specialties except paediatrics and orthopaedics. Six intensive
care units (medical ICU, general, thoracic and transplant
surgery ICU, trauma ICU, burn ICU, cardiac surgery ICU,
neurosurgery ICU) with a total of 65 (...truncated)