Urinary tract infection and pyelonephritis: SAQ

This febrile infant has a positive dipstick with both leucocyte esterase and nitrites, which makes urinary tract infection highly likely, and the absence of another focus places pyelonephritis at the top of the differential. Because she is irritable but alert with good perfusion, she is a candidate for oral therapy after the urine culture is confirmed, but the threshold to sample urine was correctly applied and the culture must guide definitive management. ^[1]

Question 1 (10 marks)

Outline your diagnostic approach, including how you would confirm the diagnosis and how you would interpret the urine results. ^[1]

The urine was correctly obtained by catheterisation, because a child under two years must have urine sampled by catheter or suprapubic aspiration rather than a bag specimen, which carries an unacceptably high contamination rate. Confirm the diagnosis by sending the catheter specimen for culture and sensitivity, and by reviewing microscopy for pyuria and bacteriuria. ^[1]

The diagnosis of UTI requires both pyuria and a significant growth of a single uropathogen. The combination of positive leucocyte esterase and nitrites on dipstick is highly predictive, but the culture threshold for a catheter specimen is a single organism growing at 50,000 colony-forming units per millilitre or greater. A positive culture without pyuria suggests contamination or asymptomatic bacteriuria and must not be treated as infection. ^[1]

Because she is under two years and febrile, this is treated as pyelonephritis rather than simple cystitis, and she is at risk of renal scarring. Obtain blood only if she appears toxic or fails to improve, but in a febrile infant under one month the standard would include blood cultures and a full sepsis evaluation. ^[1]