The impact of revised CLSI cefazolin breakpoints on the clinical outcomes of Escherichia coli bacteremia.

BACKGROUND/PURPOSE: The susceptibility breakpoints of cephalosporins for Enterobacteriaceae were revised by the Clinical and Laboratory Standards Institute (CLSI) in 2010 and 2011. The clinical outcome and susceptibility data were analyzed to evaluate the impact of revised CLSI cefazolin breakpoints on the treatment of Escherichia coli bacteremia. METHODS: Forty-three bacteremic Escherichia coli isolates from Taichung Veterans General Hospital, Taichung, Taiwan, during the period from January 2013 to December 2013, were selected to analyze the minimum inhibitory concentration (MIC) distributions of cefazolin and the correlated clinical responses to cefazolin therapy. RESULTS: The modal cefazolin MIC among the 43 isolates was 1 µg/mL and accounted for 18 (42%) isolates. The cumulative percentage for MICs ≤ 2 µg/mL was 79%. The conventional dosing regimens achieved clinical cure in 33 (97%) of 34 patients with bacteremia due to E. coli with a cefazolin MIC ≤ 2 µg/mL, in all of the six patients with a cefazolin MIC of 4 µg/mL, and all of the three patients with a cefazolin MIC of 8 µg/mL. CONCLUSION: The microbiological data support the revised CLSI breakpoints of cefazolin. The conventional cefazolin dosing regimens can still achieve satisfactory clinical cure rates for bacteremia of E. coli with a cefazolin MIC ≤ 2 µg/mL in patients without severe septic shock. Before the approval of the efficacy of cefazolin for the treatment of E. coli isolates with a cefazolin MIC of 4 µg/mL, it is prudent to use cefazolin only when a high drug level can be achieved in the infection site, such as the urinary tract.