While trimethoprim-sulfamethoxazole (TMP-SMX) is recommended as one of the first-line empiric therapies for treatment of acute uncomplicated cystitis, institutions that observe resistance rates exceeding 20% for Escherichia coli (E. coli) should utilize alternative empiric antibiotic therapy per the Infectious Diseases Society of America (IDSA). Identifying risk factors associated with TMP-SMX resistance in E. coli may help guide empiric antibiotic prescribing for urinary tract infections (UTIs).

This multicenter, retrospective study included adult patients who were discharged from 12 emergency departments (EDs) with a urine culture positive for E. coli between January 1, 2019 and December 31, 2019. Logistic regression was used to assess the relationship between potential risk factors and TMP-SMX resistance. The overall institutional antimicrobial resistance rates for E. coli were compared to the rates seen in the study population of ED urinary isolates.

Among 427 patients included from a randomized sample of 500 with a urine culture positive for E. coli, 107 (25.1%) were resistant to TMP-SMX. Three predictors of TMP-SMX resistance were identified: recurrent UTI (OR 2.27 [95% CI 1.27–3.99]), genitourinary abnormalities (OR 2.31 [95% CI 1.17–4.49]), and TMP-SMX use within 90 days (OR 8.77 [95% CI 3.19–28.12]). When the antibiotic susceptibilities for this ED cohort were compared to the institutional antibiogram, the TMP-SMX resistance rate was found to be higher in the ED population (25.1% vs 20%).

TMP-SMX should likely be avoided as first-line therapy for UTI in patients who have recurrent UTIs, genitourinary abnormalities, or have previously received TMP-SMX within the past 90 days. The use of an ED-specific antibiogram should be considered for assessing local resistance rates in this population.