Contamination of urinary cultures in initial-stream versus later-stream urine in children undergoing bladder catheterization for the diagnosis of urinary tract infection

Background: Urine cultures obtained by bladder catheterization can be contaminated by bacteria colonizing the distal urethra. Data are inconclusive regarding the potential advantage of discarding the first few urine drops obtained by bladder catheterization and testing only the sample of late-stream urine, thus reducing the likelihood of urine culture contamination. Aim: The aim of this study was to evaluate whether the incidence of contaminated urine cultures obtained by bladder catheterization can be reduced by splitting urine samples into ‘initial’ and ‘late’ samples and using only ‘late’ samples for culture. Methods: Urine samples obtained by bladder catheterization from children younger than 2 years being evaluated for urinary tract infection were prospectively collected. Quantitative culture results were compared between initial-stream and late-stream urine samples. Results: A total of 199 urine culture pairs of initial and late samples were compared. When using a cutoff value of at least 10 000 colony forming units/ml, late samples were superior to the initial ones in reducing contamination of urine cultures (P=0.029). Conclusion: When obtaining urine cultures by bladder catheterization in children younger than 2 years, discarding the first few urine drops and using only the late stream for culture reduces false-positive culture results and improves the accuracy of urinary tract infection diagnosis.

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