Urinary Tract Infection: Imaging Follow-Up
A 3-year-old boy was admitted 5 days ago with fever of 39.6 °C, vomiting, and loin tenderness. Urine culture grew more than 100000 colony-forming units per mL of Escherichia coli and his fever resolved on intravenous antibiotics. This was his first documented urinary tract infection, serum creatinine has remained normal, blood pressure is 96/58 mm Hg, and there is no antenatal hydronephrosis. Which is the most appropriate next investigation?
- A.Renal and bladder ultrasonographyCorrect
- B.Micturating cystourethrography
- C.Contrast-enhanced abdominal computed tomography
- D.Long-term low-dose antibiotic prophylaxis
Explanation
Renal and bladder ultrasonography is the first-line imaging study after a first febrile urinary tract infection in a young child, because it is non-invasive, free of ionising radiation, and detects the abnormalities that most change management: hydronephrosis, duplex systems, ureteric dilatation, renal scarring, bladder wall thickening, and significant post-void residual volume. It is the gateway test whose result determines whether any further imaging is needed. Micturating cystourethrography, which delivers bladder catheterisation and radiation, is reserved for defined indications: atypical infection, meaning a non-Escherichia coli organism, poor urine flow, septicaemia, a palpable bladder or abdominal mass, raised creatinine, or failure to respond within 48 hours; recurrent infection; or an abnormal ultrasound showing hydronephrosis or scarring. This boy had a typical Escherichia coli infection that responded promptly, so a cystourethrogram is not indicated unless the ultrasound is abnormal. Computed tomography with contrast delivers a substantial radiation dose and adds nothing over ultrasound in uncomplicated pyelonephritis; it is reserved for suspected renal abscess or complications not resolved by ultrasound. Continuous antibiotic prophylaxis is not given routinely after a single uncomplicated infection, since trials show limited benefit against renal scarring and it promotes resistance; it is considered mainly in high-grade vesicoureteric reflux or recurrent febrile infections. A dimercaptosuccinic acid scan may be used later to assess established scarring, ideally at least 4 to 6 months after the acute episode.
Why each option
- A.
- Correct. Ultrasonography is the first-line study after a first febrile urinary tract infection and determines whether further imaging is needed.
- B.
- A micturating cystourethrogram is reserved for atypical or recurrent infection or an abnormal ultrasound, none of which applies here.
- C.
- Contrast computed tomography adds radiation without benefit over ultrasound in uncomplicated pyelonephritis.
- D.
- Routine long-term prophylaxis after a single uncomplicated infection is not supported and encourages resistant organisms.
Reference: NICE Guideline NG224, Urinary Tract Infection in Under 16s, 2022; AAP Clinical Practice Guideline, reaffirmed 2024
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