2238. Effect of Cefazolin Breakpoint Update in Susceptibility Reports on Antimicrobial Use

Abstract Background The Clinical Laboratory Standards Institute updated the breakpoints for cefazolin in the treatment of E. coli, Klebsiella, and Proteus (EKP) infections in 2011 to reflect doses used in clinical practice and achievable therapeutic concentrations in different body sites (urine vs. non-urine). The UTMB clinical microbiology laboratory adopted this update in January 2022 with the introduction of MicroScan™ technology. Our objective was to evaluate the effect of the cefazolin breakpoint update on antimicrobial use in EKP bloodstream infections. Methods This was a retrospective, multicenter, pre-post, study conducted at four UTMB hospitals. Pre-intervention data was collected from January 2021 to December 2021 and post-intervention data was collected from February 2022 to March 2023. Patients ≥ 18 years old were included if they were admitted to a UTMB hospital and received antibiotics for EKP bacteremia. Texas Department of Criminal Justice patients, those with beta-lactam anaphylaxis, polymicrobial bacteremia, immunocompromised patients, and Klebsiella aerogenes isolates were excluded. The primary outcome was cefazolin days of therapy (DOTs) for EKP bacteremia. Extended-spectrum beta-lactamase (ESBL)-producing isolates and Clostridioides difficile (C. difficile) infection six months after the index admission, and in-hospital and 28-day mortality were also assessed. Results There were 50 and 48 patients included in the pre- and post-intervention periods, respectively. Most patients were female (59%) with a mean age of 67.8 years (standard deviation [SD] 14.9). The most isolated gram-negative pathogen was Klebsiella pneumonia (81%) followed by Proteus mirabilis (13%) from urinary sources of infection (59%). There was no significant difference in median cefazolin DOTs before (0 days; interquartile range [IQR] 0,0) and after (0 days; IQR 0,0) the breakpoint update (p=0.35). There was no difference in ESBL-producing pathogens (2 vs. 3, p=0.67), C. difficile infection (1 vs. 2, p=0.61), in-hospital (3 vs. 7, p=0.20), or 28-day mortality (0 vs. 0, p=1) between the pre- and post-breakpoint update groups. Conclusion Updating the breakpoint to a lower value for EKP isolates in the blood did not have an effect on cefazolin use. Disclosures All Authors: No reported disclosures