🔑 Key Learning

  • Most commonly caused by E. coli (90%)
  • Atypical and recurrent UTIs require imaging per NICE guidelines
  • Infants <3 months with suspected UTI require urgent admission
  • Urine dip and MCS guide management in older children
  • Recurrent UTIs may require prophylaxis and imaging (US, DMSA)

🧬 Pathophysiology

  • Caused by ascending infection of the urinary tract
  • E. coli is the most common pathogen
  • A UTI is considered recurrent if:
    • 3 or more LUTI
    • 2 or more UTI (at least one of which was UUTI)
  • A UTI is considered atypical if:
    • Serious illness / sepsis/ AKI
    • Poor urine flow, abdominal/bladder mass
    • Failure to respond to appropriate ABx
    • Non-E. Coli organism (e.g. proteus, staphylococcus, pseudomonas) 

👀 Clinical Features

In children < 3 months:

  • Pyrexia with no other source
  • Vomiting, poor feeding
  • Irritability, lethargy
  • Failure to thrive

In children > 3 months:

  • Fever, dysuria, urinary frequency
  • Abdominal/flank pain
  • Cloudy, malodorous urine
  • Changes in continence (e.g. bedwetting)
  • Macroscopic haematuria

🧪 Investigations and Referral

  • Use NICE traffic light system to assess severity
  • < 3 months with suspected UTI: Urgent referral for IV antibiotics, urine MCS
  • > 3 months: Urine dipstick
    • Treat if leukocytes + nitrites OR nitrites alone
    • Send MCS in all cases

Suspected Pyelonephritis

  • Fever > 38°C and/or loin pain
  • Send urine MCS
  • Consider paediatric referral
  • Diagnose if: fever + bacteriuria ± loin pain

💊 Management

Antibiotics

  • Pyelonephritis (>3 months): PO cefalexin
  • LUTI (>3 months):
    • 1st line: Trimethoprim or nitrofurantoin
    • 2nd line: Amoxicillin (if sensitive), cefalexin
  • Suspected UTI <3 months: Admit for IV antibiotics

🧠 Imaging

Ultrasound

  • During acute infection: if atypical features or poor response
  • Within 6 weeks if:
    • First UTI in <6 months
    • Recurrent UTI in >6 months

DMSA Scan (4–6 months post-infection)

  • To assess renal scarring
  • Indicated in:
    • <3 years with atypical UTI
    • Any child with recurrent UTIs

🔁 Recurrent UTI

  • Definition:
    • ≥3 LUTIs OR
    • ≥2 UTIs (one being upper)
  • Management:
    • Consider prophylactic antibiotics (trimethoprim, nitrofurantoin)
    • Arrange US and DMSA

🔄 Vesicoureteral Reflux (VUR)

🧬 Pathophysiology

  • Retrograde urine flow from bladder to ureters
  • Most cases due to abnormal vesicoureteric junction development

👀 Clinical Impact

  • Increases risk of recurrent UTI and renal scarring

🧪 Investigation

  • Micturating cystourethrogram (MCUG):
    • Radiocontrast is administered into the bladder via a urinary catheter
      • Reflux is identified on imaging, during voiding
    • Indications:
      • For <6 months with atypical/recurrent UTI
      • Consider if poor flow, dilatation, FHx VUR, non-E. Coli UTI

💊 Management

  • Prophylactic antibiotics
  • Surgical: STING procedure, ureteric reimplantation

📝 Exam Clues & Clinchers

  • Pyrexia with no source in <3 months → Suspect UTI → urgent referral
  • Fever > 38.0 + flank pain → Suggests pyelonephritis
  • Ultrasound if UTI < 6 months or >6 months with recurrent UT
  • Recurrent UTI or atypical infection in <3yrs → Requires DMSA scan

🔗 Useful Links and References