1549. Impact of New Fluoroquinolone Breakpoints on Enterobacteriaceae Susceptibility Rates and Clinical Outcomes

BACKGROUND: In January 2019, the Clinical and Laboratory Standards Institute (CLSI) lowered the Fluoroquinolone (FQ) susceptibility breakpoints for Enterobacteriaceae. The new breakpoints were updated primarily based on FQ pharmacodynamics, and only limited clinical data. We sought to evaluate clinical outcomes among patients who received an FQ for infection with Enterobacteriaceae with MIC values that would now be considered resistant, using the new interpretive criteria. We also assessed the potential impact of the new breakpoints on overall blood and urine Enterobacteriaceae susceptibility rates at our medical center. METHODS: All positive blood and urine cultures with Enterobacteriaceae between September 1, 2018 and February 28, 2019 were included. Enterobacteriaceae isolates with ciprofloxacin MICs of 0.5 and 1 µg/mL (based on new breakpoints, now considered non-susceptible) were identified. We assessed the length of stay (LOS), mortality, and 30-day readmissions among patients who received an FQ for treatment. The impact of the new breakpoints on overall Enterobacteriaceae susceptibilities from urine and blood isolates was also determined. RESULTS: A total of 1,761 cultures (191 blood, 1,570 urine) grew Enterobacteriaceae. One-hundred and twenty-five (7%) cultures grew isolates with a ciprofloxacin MIC of 0.5 or 1 µg/mL. Eighteen patients with Enterobacteriaceae isolated (4 blood, 14 urine) received an FQ. Among these patients, the median LOS was 4 days; one patient was readmitted within 30 days, and 0% mortality was observed. The patient readmitted within 30 days received an FQ for a blood isolate with MIC 0.5. Overall, with the revised breakpoints, we observed a 4.2% decrease in the number of Enterobacteriaceae that would be susceptible to ciprofloxacin (Figure 1). CONCLUSION: The new FQ breakpoints for Enterobacteriaceae will have a marginal impact on overall FQ susceptibility rates at our medical center. In this single-center study, patients that received FQ antibiotics for Enterobacteriaceae with MIC values now considered intermediate or resistant did not appear to experience poor outcomes. [Image: see text] [Image: see text] DISCLOSURES: All authors: No reported disclosures.