BACKGROUND: A patient's prior urine cultures are often considered when choosing empiric antibiotic therapy for a suspected urinary tract infection.
We sought to evaluate how well previous urine cultures predict the identity and susceptibility of organisms in a patient's subsequent urine cultures.
METHODS: We conducted a multinational, multicenter, retrospective cohort study, including 22 019 pairs of positive urine cultures from 4351 patients across 2 healthcare systems in Toronto, Ontario, and Chicago, Illinois. We examined the probability of the same organism being identified from the same patient's positive urine culture as a function of time elapsed from the previous positive urine specimen; in cases where the same organism was identified we also examined the likelihood of the organism exhibiting the same or better antimicrobial susceptibility profile.
RESULTS: At 4-8 weeks between cultures, the correspondence in isolate identity was 57% (95% confidence interval [CI], 55%-59%), and at >32 weeks it was 49% (95% CI, 48%-50%), still greater than expected by chance (P < .001). The susceptibility profile was the same or better in 83% (95% CI, 81%-85%) of isolate pairs at 4-8 weeks, and 75% (95% CI, 73%-77%) at >32 weeks, still greater than expected by chance (P < .001). Despite high local rates of ciprofloxacin resistance in urine isolates across all patients (40%; 95% CI, 39.5%-40.5%), ciprofloxacin resistance was < 20% among patients with a prior ciprofloxacin sensitive organism and no subsequent fluoroquinolone exposure.
CONCLUSIONS: A patient's prior urine culture results are useful in predicting the identity and susceptibility of a current positive urine culture. In areas of high fluoroquinolone resistance, ciprofloxacin can be used empirically when prior urine culture results indicate a ciprofloxacin-susceptible organism and there has been no history of intervening fluoroquinolone use.
MacFadden DR, Ridgway JP, Robicsek A, Elligsen M, Daneman N. Are you the author?
Department of Medicine, University of Toronto; Department of Medicine, University of Chicago; Department of Medicine, NorthShore University HealthSystem, Evanston, Illinois; Department of Medicine, Division of Infectious Diseases, Sunnybrook Health Sciences Centre; Department of Medicine, University of Toronto; Department of Medicine, Division of Infectious Diseases, Sunnybrook Health Sciences Centre Insitute for Clinical Evaluative Sciences, Toronto, Ontario, Canada.
Reference: Clin Infect Dis. 2014 Nov;59(9):1265-71.