title: Predictive utility of prior positive urine cultures.
abstract: 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.
authors.affiliation: Department of Medicine, University of Toronto.
authors.forename: Derek R
authors.initials: DR
authors.lastname: MacFadden
authors.affiliation: Department of Medicine, University of Chicago.
authors.forename: Jessica P
authors.initials: JP
authors.lastname: Ridgway
authors.affiliation: Department of Medicine, University of Chicago Department of Medicine, NorthShore University HealthSystem, Evanston, Illinois.
authors.forename: Ari
authors.initials: A
authors.lastname: Robicsek
authors.affiliation: Department of Medicine, Division of Infectious Diseases, Sunnybrook Health Sciences Centre.
authors.forename: Marion
authors.initials: M
authors.lastname: Elligsen
authors.affiliation: 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.
authors.forename: Nick
authors.initials: N
authors.lastname: Daneman
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001419:Bacteria / Q000187:drug effects / Q000302:isolation & purification; D001437:Bacteriuria / Q000175:diagnosis / Q000453:epidemiology / Q000382:microbiology; D002641:Chicago / Q000453:epidemiology; D002939:Ciprofloxacin / Q000494:pharmacology; D003428:Cross Infection / Q000453:epidemiology / Q000382:microbiology; D024881:Drug Resistance, Bacterial; D005260:Female; D006801:Humans; D008297:Male; D008826:Microbial Sensitivity Tests; D008875:Middle Aged; D009864:Ontario / Q000453:epidemiology; D012189:Retrospective Studies; D014552:Urinary Tract Infections / Q000453:epidemiology / Q000382:microbiology
chemical_list: D000900:Anti-Bacterial Agents; D002939:Ciprofloxacin
keywords: antimicrobial resistance; nosocomial infection; stewardship