Key Facts

UTI in children is important because of the risk of renal scarring, particularly in young children with vesicoureteral reflux. Prompt diagnosis and treatment, followed by appropriate imaging, reduce the risk of long-term renal damage.

Epidemiology

UTI is one of the most common bacterial infections in children. By age 7: ~8% of girls and ~2% of boys have had at least one UTI. Recurrence rate: ~30% in first year. UTI is the most common cause of fever without source in infants <2 years.

Aetiology

• E. coli: ~80% (commonest at all ages)
• Proteus mirabilis: More common in boys (associated with phimosis/foreskin)
• Klebsiella, Enterococcus, Pseudomonas: Less common; consider if atypical or recurrent
• Risk factors: Female sex, constipation, dysfunctional voiding, VUR, posterior urethral valves (boys), neuropathic bladder, immunosuppression

Pathophysiology

Most childhood UTIs result from ascending infection from the perineum via the urethra to the bladder (cystitis) and potentially to the kidneys (pyelonephritis). VUR allows retrograde flow of urine from the bladder into the ureters/renal pelvis, increasing the risk of pyelonephritis and renal scarring. Renal scarring results from the inflammatory response to infection in the renal parenchyma, particularly in young children with immature kidneys.

Infants (<3 Months)

• Non-specific: Fever, irritability, poor feeding, vomiting, jaundice, failure to thrive
• Sepsis presentation possible
• NO localising urinary symptoms

Infants and Toddlers (3 Months-3 Years)

• Fever (may be the only symptom)
• Irritability, vomiting, poor feeding
• Offensive/cloudy urine
• Abdominal pain

Older Children (>3 Years)

• Dysuria, frequency, urgency
• Abdominal or loin pain
• Enuresis (new onset in previously dry child)
• Fever, vomiting (suggests pyelonephritis)

Red Flags

• Infant <3 months with UTI — admit for IV antibiotics
• Sepsis features (poor perfusion, altered consciousness) — treat as sepsis
• Poor urine flow or palpable bladder — consider posterior urethral valves (boys)
• Raised creatinine — investigate for obstructive uropathy
• Non-E. coli organism — suggests structural abnormality

Urine Collection

• Clean catch: Preferred method — first-line for all ages
• Suprapubic aspiration (SPA): Gold standard in infants <3 months
• In-out catheter: Alternative to SPA
• Bag specimen: High contamination rate (~60%) — only use for dipstick screening; NOT for culture

Urine Analysis

• Dipstick: Nitrites (specific) and leucocyte esterase (sensitive); both positive — treat as UTI
• Microscopy: WCC (pyuria) and bacteria
• Culture: Gold standard — >10⁵ CFU/mL single organism (clean catch); any growth from SPA is significant

Bloods

• FBC, CRP, U&Es: If pyelonephritis or sepsis suspected
• Blood culture: If sepsis suspected

Imaging (NICE CG54)

Responds to treatment within 48h, typical UTI, age >6 months:

• No imaging needed for first UTI

Atypical UTI (any age):

• USS within 6 weeks; DMSA at 4-6 months

Recurrent UTI:

• USS within 6 weeks; DMSA at 4-6 months; MCUG if <6 months or dilated urinary tract or poor urine flow

Age <6 months with first UTI:

• USS within 6 weeks; DMSA at 4-6 months (if atypical or recurrent → add MCUG)

Pharmacological

Lower UTI (cystitis):

• Trimethoprim 4mg/kg BD for 3 days (first-line) OR nitrofurantoin 1mg/kg QDS OR cefalexin 12.5mg/kg BD
• Adjust per local antibiogram

Upper UTI (pyelonephritis/febrile UTI):

• Oral: Cefalexin 12.5mg/kg BD for 7-10 days (or co-amoxiclav)
• IV (if <3 months, sepsis, vomiting): Ceftriaxone 80mg/kg OD or co-amoxiclav 30mg/kg TDS for 2-4 days → switch to oral when improving

Prophylactic antibiotics:

• Consider for recurrent UTI or significant VUR: Trimethoprim 2mg/kg ON or nitrofurantoin 1mg/kg ON

Non-pharmacological

• Adequate fluid intake: Encourage regular drinking
• Regular voiding: Timed voiding, double voiding
• Treat constipation: Very commonly contributes to UTI recurrence
• Hygiene: Front-to-back wiping in girls

Referral Criteria

• Atypical UTI — paediatric assessment + imaging
• Recurrent UTI (≥2) — paediatric assessment + imaging
• Abnormal imaging — paediatric nephrology/urology
• Infant <3 months — admission for IV antibiotics
• Suspected structural abnormality (poor flow, palpable bladder) — paediatric urology

• Uncomplicated UTI: Full resolution with appropriate antibiotics
• Recurrence: ~30% in first year after initial UTI
• Renal scarring: ~5-15% of children with febrile UTI; higher with VUR, delayed treatment, recurrent infections
• VUR: Grades I-III often resolve spontaneously; grades IV-V may require surgery
• Long-term: Renal scarring can lead to hypertension, proteinuria, and CKD; important cause of paediatric hypertension

NICE CG54 Imaging Guide

Atypical UTI Definition (NICE)