Urinary tract infection and pyelonephritis: Viva

Branch 1: Recognising the problem and the sampling decision

The candidate should immediately recognise that this febrile toddler with a positive dipstick has presumptive urinary tract infection, and because he has fever rather than isolated dysuria, he should be treated as having pyelonephritis until proven otherwise. The absence of another focus of fever in a child under two years is itself the trigger to sample urine, and the positive leucocyte esterase and nitrites together make UTI highly likely. ^[1]

The examiner will probe the sampling method. The candidate must state that a child under two years must have urine obtained by urethral catheterisation or suprapubic aspiration, because bag specimens have a contamination rate so high that a positive result cannot be trusted and leads to overdiagnosis and unnecessary imaging. The specimen was correctly obtained by catheterisation, and the principle is that the urine must be sampled before any antibiotic is given, because prior antibiotics permanently blunt the culture yield. ^[1]