Antimicrobial susceptibility of Escherichia coli in uncomplicated cystitis in the emergency department: is the hospital antibiogram an effective treatment guide?

OBJECTIVES: The objective was to compare the rates of antimicrobial susceptibility in strains of Escherichia coli isolated from uncomplicated cystitis cases presenting to the emergency department (ED) of a tertiary care center to those reported on that institution's hospital-wide antibiogram. The hypothesis was that cases of uncomplicated cystitis presenting to the ED will exhibit higher antimicrobial susceptibility than is reported by the hospital-wide antibiogram.

METHODS: A retrospective chart review of patients who were diagnosed with uncomplicated cystitis in the ED of a large, academic tertiary care center was conducted. Due to an error in the implementation of a new electronic medical record system at this institution in 2009, all urine samples with any abnormality were reflexively sent for culture. The authors were then able to review and record the antibiotic susceptibility patterns of all cultures that grew E. coli. Exclusion criteria included fever, subsequent hospital admission, treatment of suspected pyelonephritis, receiving current cystitis treatment, male sex, indwelling catheters, recent surgery or hospitalization, or asymptomatic for cystitis. Culture isolate antimicrobial susceptibility was then compared with the hospital-wide antibiogram of the same period. Empiric treatment regimens were also recorded as secondary data.

RESULTS: Greater susceptibility to trimethoprim-sulfamethoxazole (TMP-SMX; 80% vs. 71%), cefazolin (97% vs. 87%), and ciprofloxacin (89% vs. 73%) was found in our population than was published in the hospital antibiogram. These differences were shown to be statistically significant using Fisher's exact test (p < 0.05). A very high sensitivity to nitrofurantoin (99%), similar to the hospital antibiogram (98%), was also found. Also noted was a high rate of antimicrobial susceptibility when specific empiric treatment was initiated with TMP-SMX or ciprofloxacin: 92 and 89%, respectively.

CONCLUSIONS: The greater susceptibility of E. coli to TMP-SMX, cefazolin, and ciprofloxacin observed in this population supports the hypothesis that antimicrobial susceptibility rates in uncomplicated cystitis presenting to the ED are greater than those reported in the hospital-wide antibiogram. This could affect treatment guidelines by confirming that antimicrobials currently recommended for use in uncomplicated cystitis are more effective in this setting than currently reported by the hospital-wide antibiogram.