Urinary Tract Infection (Paediatrics)

Summary

Urinary Tract Infection (UTI) is the most common serious bacterial infection in children. It ranges from benign Cystitis to life-threatening Pyelonephritis. The Stakes: In children <2 years, the growing kidney is highly susceptible to Renal Scarring from infection. This can lead to permanent hypertension and CKD in adult life. The Challenge: Diagnosis is difficult. A 5-month-old cannot say "it hurts when I pee". They present with ambiguous "Fever of Unknown Origin".

Clinical Pearls

The "Silent" Pyelonephritis: In infants, fever may be the only sign. The classic triad (dysuria/frequency/flank pain) is rare below age 5. Constipation is King: 80% of recurrent UTIs are driven by functional constipation ("The Rectum compresses the Bladder"). Always treat the bowel. Bag vs Catch: A positive "Bag Urine" means nothing (high contamination). A negative bag rules it out. Positive bag -> Confirm with Catheter or Clean Catch.

Mechanism

1. Colonisation: Perineal flora (E. Coli) colonise the urethra.
2. Ascension: Bacteria climb into bladder (Cystitis).
3. Reflux (VUR): Incompetent valves allow urine to shoot up ureters to the kidney during voiding.
4. Pyelonephritis: Bacterial invasion of renal parenchyma -> Inflammation -> Scarring.

Vesicoureteric Reflux (VUR)

Graded I-V.

• Grade I: Ureter only.
• Grade V: Massive dilation, tortuosity, loss of papillary impressions.
• See Image Manifest for Grading Diagram.

Managing UTI depends entirely on these definitions. Memorise them.

Atypical UTI (The "Red Flag" UTI)

Any of:

1. Seriously ill (Sepsis).
2. Poor urine flow (Obstruction).
3. Abdominal or Bladder mass.
4. Raised Creatinine.
5. Septicaemia.
6. Failure to respond to antibiotics within 48 hours.
7. Infection with Non-E. Coli organisms.

Recurrent UTI

• 2 or more episodes of Pyelonephritis.
• 1 episode of Pyelonephritis + 1 episode of Cystitis.
• 3 or more episodes of Cystitis.

1. The "Dysuria" Differential

Most children who say "it hurts to pee" do NOT have a UTI.

• Vulvovaginitis: Commonest cause in girls. Redness of vulva due to soap/bubble bath irritants or poor hygiene.
  • Clue: Pain is external ("stinging" on skin). Urinalysis negative (or leucocytes only).
• Balanitis: Inflammation of the glans penis in boys.
• Threadworms: Nocturnal itching leads to scratching and urethral irritation.
• Sexual Abuse: Always consider in unexplained recurrent symptoms or behavioural changes.

2. The "Fever without Focus" Differential

In a febrile infant with no cough/coryza:

• Meningitis: Bulging fontanelle, irritability.
• Pneumonia: Tachypnoea, recessions. (Silent chest).
• Kawasaki Disease: Prolonged fever > 5 days. (Sterile Pyuria is common!).
• Otitis Media: Red tympanic membrane.

3. The "Abdominal Pain" Differential

• Appendicitis: RIF pain.
• Mesenteric Adenitis: History of recent URI.
• Constipation: Palpable faecal loading. (Also a cause of UTI).

1. Acute Pyelonephritis (Admit)

Indication: Age < 3 months, Sepsis, or Vomiting.

• Access: IV Cannula essential. If difficult, consider Intraosseous (IO) in shock.
• Antibiotics:
  • Ceftriaxone: 50-80 mg/kg ONCE daily. (First line in many units).
    • Pros: Once daily, broad spectrum, CSF penetration.
    • Cons: Calcium precipitation (avoid with Calcium infusions), Biliary sludge.
  • Amoxicillin + Gentamicin: The Neonatal Standard.
    • Gentamicin: 5-7 mg/kg ONCE daily.
    • Monitoring: Must check "Trough" levels before 2nd dose to avoid Ototoxicity/Nephrotoxicity.
• Fluids: Maintenance IV fluids (0.9% Saline + 5% Dextrose) until drinking.

2. Acute Pyelonephritis (Oral / Home)

Indication: Age > 3 months, Systemically well, Tolerating orals.

• Choice A: Co-amoxiclav (Amoxicillin + Clavulanic Acid).
  • Dose: see local formulary (usually 0.25ml/kg of 125/31 suspension).
  • Spectrum: Covers E. Coli, Klebsiella.
• Choice B: Cefalexin.
  • Pros: Tastes better (strawberries) than Co-amoxiclav.
  • Cons: Clostridium Difficile risk? (Low in kids).
• Duration: 7-10 Days. (Short courses fail in pyelonephritis).

3. Lower UTI (Cystitis)

Indication: Dysuria, Frequency, No Fever.

• Choice A: Trimethoprim.
  • Resistance: Rising (30% of E. Coli are resistant in UK).
  • Use: Only if local resistance is low.
• Choice B: Nitrofurantoin.
  • Contraindication: Renal Impairment (Needs good GFR to concentrate in urine). G6PD Deficiency.
  • Pros: Very low resistance rates.
  • Duration: 3 Days.
• Choice C: Cefalexin.

You cannot cure Recurrent UTI without curing Constipation. The Rectum-Bladder interaction: A loaded rectum pushes the bladder anteriorly, causing instability and incomplete emptying (stasis = infection).

• Laxatives: Movicol (Macrogol) is First Line.
• Disimpaction: High dose escalating regimen if faecal loading is palpable.

• Note: Avoid Cefalexin if possible (C. Diff risk), but it is very effective for bugs.

This table determines the workflow. It is designed to expose the minimum number of children to invasive radiation, while catching those at risk.

1. Renal Ultrasound (USS)

• Purpose: Anatomic screen.
• Looks for: Hydronephrosis, Dilated ureters, Bladder wall thickness.
• Pros: No radiation. Non-invasive.
• Cons: Cannot see scarring. Cannot see mild reflux.

2. DMSA Scan (Dimercaptosuccinic Acid)

• Purpose: The "Gold Standard" for Renal Scarring and Function.
• Technique: Radio-isotope (Technetium-99) is injected. It binds to the proximal tubules. A Gamma camera takes pictures.
• Timing: Must be done 4-6 months after the acute infection.
  • Why? Acute inflammation looks like a defect ("Cold Spot"). You wait for inflammation to settle to see if permanent scarring remains.
• Result: "Split Function" (e.g., Left 50% / Right 50% is normal. Left 10% / Right 90% is a dead kidney).
• Radiation: Equivalent to ~4 months of background radiation.

3. MCUG (Micturating Cystourethrogram)

• Purpose: The "Gold Standard" for Vesicoureteric Reflux (VUR).
• Technique:
  1. Catheterise the child (traumatic).
  2. Fill bladder with contrast.
  3. Child must void (pee) on the table under fluoroscopy.
• Indication: Only for <6 months with Atypical/Recurrent features.
• Prophylaxis: Child requires 3 days of antibiotics (Trimethoprim) around the procedure to prevent iatrogenic sepsis.

4. MAG3 Renogram

• Purpose: To assess Obstruction (PUJ obstruction).
• Technique: Similar to DMSA but dynamic. Watch the tracer flow out of the kidney. Use Furosemide to wash it out.
• Curve: Is it obstructive or dilated?

So you found Reflux. Now what?

The "Maturation" Theory

• Most mild VUR (Grade I-III) resolves spontaneously as the child grows. The ureter tunnel through the bladder wall lengthens.
• Management: Conservative. Treat constipation. Prompt treatment of UTIs.

Antibiotic Prophylaxis

• Controversial. NICE NG54 generally says NO. (Does not prevent scarring, breeds resistance).
• Exception: High grade VUR (IV-V) or Recurrent Symptomatic UTIs. Use Trimethoprim or Nitrofurantoin low dose at night.

Surgical Options

1. Deflux Injection (Endoscopic): Injecting a gel bulking agent around the ureteric orifice to tighten the valve. Success 70-80%.
2. Ureteric Reimplantation (Open Surgery): Chopping the ureter and replanting it with a longer tunnel. Success 98%. Big operation.

1. Renal Scarring (Reflux Nephropathy)

• Risk Window: The kidney is most vulnerable in the first 2 years of life.
• Mechanism: Infected urine shoots up (Reflux) -> Enters the collecting ducts (Intra-renal reflux) -> Triggers inflammation -> Fibrosis.
• Result: The renal cortex thins. The kidney stops growing (Small kidney).
• Consequence:
  • Hypertension: The scarred kidney releases Renin. (Renal Hypertension).
  • Proteinuria: Glomerular damage.
  • CKD: Progression to failure in adulthood, especially in pregnancy.

2. Urosepsis

• Infants have poor immune localisation. Pyelonephritis can rapidly become Septicaemia.
• Mortality: Significant if missed in <3 months.

3. Renal Abscess

• Rare. Prolonged fever despite antibiotics. Needs USS/CT.

OSCE Station: Explaining the DMSA Scan

Scenario: Parent asks "Why does he need a radioactive scan? Is it dangerous?" Candidate:

1. Validate: "I understand your concern about radiation."
2. Explain the Why: "We need to check if the infection has left any scars on the kidney. An ultrasound cannot see scars. Only this scan can."
3. Explain the Risk: "The amount of radiation is very small. It is equivalent to about 4 months of natural background radiation (or a flight to New York)."
4. The Benefit: "If we find a scar, we can monitor his blood pressure as he grows up to prevent kidney damage. If we don't know, we can't protect him."

Viva: The "Atypical" Definition

Examiner: "Define Atypical UTI according to NICE." Candidate: "It includes: Serious illness, Poor urine flow, Abdominal mass, Raised creatinine, Septicaemia, failure to respond in 48h, or Non-E.coli organism."

Case 1: The "Silent" Pyelonephritis

History: 4-month-old boy. Fever for 3 days. No cough/cold. Eating slightly less. Exam: Cap refill 2s. Irritable when handled. Abdomen soft. Ix: Urine Bag +ve Leucocytes. Decision: Bag is unreliable. Action: Clean Catch (CCU) obtained. Microscopy showed >100 WBC. Dx: UTI (Pyelonephritis given fever). Mx: Admitted for IV Ceftriaxone (Age > 3m but looked septic). Outcome: Recovered. USS done at 2 weeks (Normal). NO further imaging needed (First typical UTI).

Case 2: The "Constipated" Recurrence

History: 4-year-old girl. 3rd UTI in 6 months. Mum says "she goes to the toilet fine". Deep History: "Does she do massive poos that block the toilet?" -> "Yes". Exam: Palpable masses in left iliac fossa (Faecal loading). Dx: Recurrent UTI secondary to Functional Constipation. Mx: Movicol paediatric plan. Prophylactic Trimethoprim for 3 months. Learning: You cannot fix the bladder until you fix the bowel.

Case 3: The "Atypical" Surprise

History: 6-month-old girl. UTI with Proteus mirabilis (Non-E. Coli). Significance: Atypical organism. Indicates possible stones or structure anomaly. Action: Acute USS (during infection). Showed Hydronephrosis. Follow-up: DMSA at 4 months confirmed scarring. MCUG showed Grade IV Reflux. Outcome: Managed with prophylaxis and eventual surgery.

1. Hygiene & Habits

• Wiping: Front to back (girls).
• Voiding: Regular timed voiding (every 3 hours) to prevent stasis.
• Fluids: Increase water intake to "flush" the system.

2. Cranberry Juice?

• Theory: Contains proanthocyanidins which stop bacteria sticking to bladder wall.
• Evidence: Cochrane review says Weak/No Evidence for prevention in children. High sugar content is a downside.

3. Circumcision

• Evidence: Strong. Reduces UTI risk by 90% in first year of life.
• Policy: Not routine on NHS, but medically valid for recurrent UTIs in boys (Balanitis xerotica obliterans).

4. Probiotics

• Theory: Restoring healthy flora.
• Evidence: Inconclusive.

1. Renal Scarring: 5% of girls, 15% of boys with first UTI.
2. Hypertension: Long term sequela of scarring.
3. Chronic Kidney Disease: Reflux Nephropathy is a leading cause of end-stage renal failure.