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Previous urine culture results may be predictive of causative organism, susceptibility
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Previous urine culture results may be predictive of the identity and susceptibility of a current positive urine culture, and may be useful in determining an appropriate regimen of antimicrobial therapy, according to recent findings.
In the multinational, multicenter, retrospective cohort study, researchers evaluated 22,019 positive urine cultures obtained from 4,351 patients at facilities in Toronto and Chicago. All corresponding positive urine cultures were collected from the same patient more than 1 day from the initial positive culture.
For each pair of cultures, the researchers calculated the proportion of corresponding isolates with the same organism identity or antibiotic susceptibility. This percentage was plotted as a function of time between specimens. The researchers further stratified the specimens according to the city from which they were collected, receipt of antimicrobial therapy intervention and organism types. They used sums of squares of species prevalence to estimate the chance of identifying a matching organism between the two specimens, and also calculated the likelihood of paired specimens having equal or superior susceptibility profiles.
The organisms most commonly identified were Escherichia coli, Klebsiella species and Pseudomonas species. The researchers found that the correspondence of organism identity at 4 to 8 weeks between cultures was 57% (95% CI, 55-59%) and the correspondence at more than 32 weeks was 49% (95% CI, 48-50%). This was a higher correspondence percentage than was predicted by the chance estimates (P<.001). At the 4- to 8-week interval between cultures, 83% of isolate pairs had the same or better susceptibility profile (95% CI, 81-85%), and 75% of the pairs had a similar or better susceptibility profile at more than 32 weeks (95% CI, 73-77%).
Although the local rates of ciprofloxacin resistance were high in urine isolates across patients (40%; 95% CI, 39.5-40.5%), this resistance was less than 20% in patients previously found to have a ciprofloxacin-sensitive pathogen and no interim exposure to fluoroquinolones.
According to the researchers, these findings suggest that the empirical use of ciprofloxacin may be a safe option, even if the regional rates of fluoroquinolone resistance are high.
“In areas of high fluoroquinolone resistance, ciprofloxacin can be used empirically when prior urine culture results indicate a ciprofloxacin-susceptible organism and no history of intervening fluoroquinolone use,” the researchers concluded.
Disclosure: The researchers report no relevant financial disclosures.
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