Effect of the 2014 Clinical and Laboratory Standards Institute urine-specific breakpoints on cefazolin susceptibility rates at a community teaching hospital

BACKGROUND: Enterobacteriaceae, which include Escherichia coli, Klebsiella pneumoniae, and Proteus mirabilis, are identified as the infectious etiology in the majority of urinary tract infections (UTIs) in community hospitals across the United States. The minimum inhibitory concentration (MIC) is a useful tool when choosing an appropriate antibacterial agent. Recent changes to the 2014 Clinical and Laboratory Standards Institute (CLSI) guidelines included reporting a urine-specific cefazolin breakpoint for enterobacteriaceae (susceptible ≤16 mcg/mL). The purpose of this study was to determine the clinical and financial impact of implementing the 2014 CLSI urine-specific breakpoints for cefazolin in a community-based teaching hospital in the Southern U.S.A. METHODS: A retrospective review of patients hospitalized from January 1, 2010 through October 1, 2014 was performed. Patients that met inclusion criteria had a documented initial clinical isolate of E. coli, K. pneumoniae, or P. mirabilis from urine cultures during each year. Descriptive statistics and two-proportion test of hypothesis were used in the analysis to compare susceptibility rates before and after implementation of the updated CLSI breakpoints for cefazolin. RESULTS: A total of 190 clinical isolates from patients were included in the study. E. coli was the most common organism isolated (63.7%), followed by K. pneumoniae (22.1%), and P. mirabilis (14.2%). 86% of the included isolates were susceptible to cefazolin using the 2010 breakpoints. Implementation of the 2014 breakpoints did not significantly impact susceptibility results for E. coli, K. pneumoniae, or P. mirabilis. CONCLUSION: Modification of breakpoints did not significantly impact susceptibility rates of cefazolin. Substituting cefazolin may decrease the overall drug cost by 77.5%. More data is needed to correlate in vitro findings with clinical outcomes using cefazolin for UTIs.