2819. Clinical Outcomes of Fosfomycin Treatment in E. coli vs. Non-E. coli Enterobacterales Urinary Tract Infection

BACKGROUND: Oral fosfomycin tromethamine is considered a first-line agent for the treatment of uncomplicated acute cystitis in women according to the national Infectious Disease Society of America (IDSA) guideline. However, non-E. coli Enterobacterales urinary tract infection (UTI) pathogens exhibit higher minimum inhibitory concentrations (MICs) for fosfomycin and limited data exist to determine whether treatment outcomes are comparable to patients being treated with fosfomycin for E.coli UTIs. The objective of this study is to compare the clinical outcomes of patients being treated with fosfomycin who have E. coli UTIs compared to non-E. coli Enterobacterales UTIs. METHODS: This was a retrospective noninferiority study of adult inpatients with a UTI who received a fosfomycin inpatient from July 15, 2020 to March 15, 2023. The primary outcome was incidence of treatment failure within 30 days of start of fosfomycin, defined by retreatment for UTI; UTI related- hospitalization, urgent care visits, and/or ambulatory visits; subsequent positive blood culture; and/or infection related mortality. One-sided test for noninferiority was used with a 20% margin. Multivaraible logistic regression analyses were conducted adjusting for age/sex, UTI severity, and prior UTIs. RESULTS: A total of 77 patients were included; 45 with E. coli UTIs and 32 with non-E. coli Enterobacterales UTIs. The majority of the patients were female (80.5%), with a median age of 67 years (IQR, 61-69), Hispanic/Latino (50.6%), had chronic kidney disease (33%), and diabetes mellitus (35%), and were admitted to a non-ICU floor (79%). The overall incidence of treatment failure was 19.5% (90% CI 12.9%-27.7%); 15.6% in those with E. coli vs. 25% in those with non-E. coli Enterobacterales UTIs (p=0.385; absolute difference 9.4%; 90% CI -7.3% to 26.2%), not meeting the criteria for non-inferiority. In multivariable analysis, E. coli vs. non-E. coli Enterobacterales UTIs did not associate with treatment failure (adjusted odds ratio, 0.66; 95% CI 0.193-2.25; p=0.505). [Figure: see text] CONCLUSION: Fosfomycin treatment for non-E. coli Enterobacterales UTIs did not meet non-inferiority criteria when compared to patients with E. coli UTIs. Further studies with larger sample sizes are required. DISCLOSURES: All Authors: No reported disclosures