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

Abstract

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.

Management of urinary tract infections in children in an era of increasing antimicrobial resistance

“…Even urine obtained from in-and-out catheterization can be contaminated, especially in an uncircumcised male. Discarding the first few drops of urine may reduce the contamination rate of catheterization samples (19).…”

Defining urinary tract infection by bacterial colony counts: a case for 100,000 colonies/ml as the best threshold

“…However, in each case, the authors (who appear to believe that SPA samples cannot become contaminated) have argued that the pairs with void-positive/SPA-negative results demonstrate urethral contamination, whilst SPA-positive/ void-negative pairs indicated that the "UTI had been missed" in the urethral specimen [13][14][15][16][17][18]. Similarly, when only the first flow from a urethral catheter sample (where the authors expected contamination might occur) grew organisms, it was called contamination, but when only the subsequent stream was culture-positive, it is assumed that the first flow sterility was due to "non-uniform bacterial excretion in different urine phases" or the "potential randomness of growth of some bacteria" [19].…”

“…Background to urethral catheter sampling Like SPAs, the AAP recommends urethral catheterisation to avoid bacterial contamination [3], but in this case they advise using a 10 5 cfu/ml threshold of a single uropathogen to diagnose UTIs [38]. Four other thresholds have been advocated on little evidence, namely 5 × 10 4 cfu/ml [19], 10 4 cfu/ml [19,34,41], 10 3 cfu/ml [18,35,[42][43][44][45], and 10 cfu/ml [46]. In addition, the AAP now also endorses discarding the first drops of catheter urine [4] with little evidence.…”

“…Two groups showed that the first drops of catheter urine were more likely to be contaminated than the subsequent stream [37,53], but these cultures were clinically irrelevant skin commensals and very light growths of uropathogens (all < 10 4 /ml). A more recent study that recommends discarding the first flow of catheter urine had multiple shortcomings including only reporting culture positivity rates at fixed threshold ranges and using biased analysis [19].…”

Urine collection devices to reduce contamination in urine samples for diagnosis of uncomplicated UTI: a single-blind randomised controlled trial in primary care

“…Patients have been advised to discard the first part of the urine stream, as this may contain the majority of the contaminants, and capture only the mid-stream for the sample. 3,4 However, this procedure is often challenging to explain and implement, with two small low quality randomised trials finding no clear evidence of benefit 5 Another solution, which is already being implemented in healthcare settings, is the use of a urine collection device (UCD). The Whizaway Midstream (Whiz, Oxford, UK) 6 uses a pressure valve system to allow the early urine stream to flow into the toilet and the midstream sample then flows into a sample bottle.…”