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Published on: May 5, 2016
Continued in vitro cefazolin susceptibility in methicillin-susceptible Staphylococcus aureus
Benjamin H Gern1, Alexander L Greninger2, Scott J Weissman1
1Department of Pediatrics, Seattle Children's Hospital, University of Washington, Seattle, WA, USA.
Objectives:
In vitro trends of cefazolin and ceftriaxone susceptibilities from pediatric clinical isolates of methicillin-susceptible Staphylococcus aureus (MSSA) between 2011 and 2016 were analyzed for surveillance.
Methods:
Our laboratory continues to use agar disk diffusion for staphylococcal susceptibilities applying Clinical Laboratory Standard Institute's 2012 breakpoints.
Results:
A total of 3992 MSSA clinical isolates in the last 6 years were analyzed for their in vitro cefazolin and ceftriaxone susceptibilities. While all MSSA isolates exhibited cefazolin susceptibilities within the "susceptible" zone range, there have been a proportion of isolates with ceftriaxone susceptibilities falling in "intermediate" zones, ranging from 2.6% in 2011 to 8.3% in 2016.
Conclusions:
Cefazolin continues to be the recommended agent for MSSA treatment at our institution, reflected by the finding that only 2% (6/321) of patients who received ceftriaxone as definitive therapy for MSSA bacteremia during the study period. We have confirmed the cefoxitin-predicted MSSA susceptibility to cefazolin, but have found concerning drifts in ceftriaxone susceptibilities by continued in vitro monitoring over the last 6 years.
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