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]

Branch 2: Confirming the diagnosis and the culture

The candidate should explain that the diagnosis of UTI requires both pyuria and a significant growth of a single uropathogen. The dipstick findings of leucocyte esterase and nitrites predict infection, but confirmation rests on the culture, with a catheter specimen threshold of 50,000 colony-forming units per millilitre of a single organism. A positive culture without pyuria suggests contamination or asymptomatic bacteriuria and must not be treated as infection. [1]

The examiner may press on the distinction between UTI and asymptomatic bacteriuria. The candidate should state that pyuria is the finding that separates true infection from colonisation, which is why the requirement is pyuria plus significant growth rather than growth alone. This distinction matters especially in catheterised children with neurogenic bladders, where asymptomatic bacteriuria is common and treating it drives resistance without benefit. [1]

Branch 3: Treatment, the route decision, and review

The candidate should outline empiric therapy and justify the route. Because this child is febrile but not toxic, and is tolerating some oral intake, oral therapy is as effective as intravenous therapy and is the correct first choice, using cefixime or amoxicillin-clavulanate for 7 to 10 days. Intravenous ceftriaxone 50 mg per kilogram daily would be reserved for the toxic or vomiting child, the infant under one to two months, or any child failing oral therapy. [2]

The examiner will probe the review and imaging strategy. The child is reviewed at 48 hours: a child who is afebrile and improving completes the course orally, while a child still febrile or unwell is reassessed for resistant organism, obstruction, or complication and imaged urgently. After a first uncomplicated febrile UTI, imaging is selective, but recurrent or atypical infection warrants ultrasound, a DMSA scan months later to detect scarring, and a micturating cystourethrogram when high-grade reflux is suspected. [3]

When the candidate is asked about prophylaxis, the response should invoke the RIVUR trial, which showed that antimicrobial prophylaxis reduces recurrent UTI in children with vesicoureteral reflux but does not prevent new renal scarring and increases the risk of resistant infection. The contemporary approach is therefore to reserve prophylaxis for children with high-grade reflux, recurrent febrile UTI, or bowel and bladder dysfunction, rather than treating all reflux reflexively. [3]