What is the recommended evaluation, antimicrobial therapy, and follow‑up imaging for a pediatric patient with a suspected urinary tract infection?

Pediatric Urinary Tract Infection: Evaluation, Treatment, and Imaging

Diagnostic Approach

Obtain urine by catheterization or suprapubic aspiration in non-toilet-trained children before starting antibiotics; never use bag specimens for culture. 1, 2

• For toilet-trained children, collect a midstream clean-catch specimen for both urinalysis and culture before initiating antibiotics 3
• Diagnosis requires both pyuria (≥5 WBC/HPF on centrifuged specimen or positive leukocyte esterase) and ≥50,000 CFU/mL of a single uropathogen on culture from catheterized specimens 1, 2
• Suprapubic aspiration is the gold standard in infants <6 months and uncircumcised boys, where catheterization contamination rates reach 43% 4, 5
• A completely normal urinalysis makes UTI unlikely, but a negative leukocyte esterase alone is insufficient to rule out infection in high-suspicion cases 6, 5

Antimicrobial Therapy

Start oral antibiotics immediately after obtaining urine culture for 7-14 days (10 days most common) for febrile UTI; reserve parenteral therapy only for toxic-appearing children, those unable to retain oral intake, or infants <3 months. 1, 2

First-Line Oral Options (Based on Local Resistance)

• Amoxicillin-clavulanate 40-45 mg/kg/day divided every 12 hours 2
• Cephalosporins (cefixime 8 mg/kg/day once daily, or cephalexin 50-100 mg/kg/day divided into 4 doses) 2, 7
• Trimethoprim-sulfamethoxazole 8 mg/kg/day (of TMP component) divided every 12 hours—only if local E. coli resistance is <10% 2, 3

Parenteral Options

• Ceftriaxone 50 mg/kg IV/IM once daily for children >3 months 2
• Ampicillin + gentamicin for neonates <28 days 2

Critical Treatment Principles

• Never use nitrofurantoin for febrile UTI/pyelonephritis—it does not achieve adequate serum/parenchymal concentrations to treat upper tract infection 2, 7
• Adjust antibiotics based on culture and sensitivity results when available 2, 3
• Consider local resistance patterns: use TMP-SMX only if resistance <10% for pyelonephritis, <20% for lower UTI 2
• Do not use amoxicillin monotherapy empirically—global surveillance shows 75% median E. coli resistance 2
• Courses shorter than 7 days are inferior for febrile UTI 1, 2

Treatment Duration by Clinical Presentation

• Febrile UTI/pyelonephritis: 7-14 days (10 days most common) 1, 2
• Non-febrile UTI/cystitis: 7-10 days 2
• Neonates <28 days: 14 days total 2

Follow-Up Monitoring

Reassess within 24-48 hours to confirm fever resolution and clinical improvement; if fever persists beyond 48 hours on appropriate therapy, evaluate for antibiotic resistance, anatomic abnormality, or abscess. 2, 3

• Instruct parents to seek prompt evaluation (within 48 hours) for any future febrile illness to detect recurrent UTI early 1, 2
• No routine scheduled follow-up visits are necessary after successful treatment of first uncomplicated UTI 2
• Early treatment within 48 hours of fever onset reduces renal scarring risk by >50% 2

Imaging Recommendations

Obtain renal and bladder ultrasound (RBUS) for all children <2 years with first febrile UTI to detect anatomic abnormalities; do NOT perform routine VCUG after first UTI. 1, 2

Renal and Bladder Ultrasound (RBUS)

• Indicated for: All febrile infants <2 years with first UTI 1, 2
• NOT routinely indicated for: Children >2 years with first uncomplicated febrile UTI that responds well to treatment 2, 7
• Timing: As soon as possible after diagnosis 8
• Purpose: Detect hydronephrosis, scarring, obstruction, or structural abnormalities 1, 2

Voiding Cystourethrography (VCUG)

• NOT recommended routinely after first UTI 1, 2
• Perform VCUG if:
  • RBUS reveals hydronephrosis, scarring, or findings suggesting high-grade VUR or obstructive uropathy 1, 2
  • Second febrile UTI occurs 1, 2
  • Fever persists >48 hours on appropriate therapy 2
  • Child is <2 months old (especially boys) 2

DMSA Scan

• NOT appropriate for immediate post-treatment evaluation 2
• Reserve for 4-6 months after infection to assess renal scarring in children with known VUR, recurrent UTI, or abnormal ultrasound 2

Additional Imaging Triggers (Any Age)

• Poor response to antibiotics within 48 hours 2, 3
• Septic or seriously ill appearance 2
• Elevated creatinine 2
• Non-E. coli organism 2
• Obstructive urine stream 2

Antibiotic Prophylaxis

Do NOT routinely prescribe antibiotic prophylaxis after first UTI or for children with VUR grades I-IV. 1, 2

• The RIVUR trial showed prophylaxis reduces recurrent UTI by 50% but does not reduce renal scarring 2
• Consider prophylaxis selectively only for high-risk patients: recurrent febrile UTI or high-grade VUR (grades IV-V) 2
• Weigh benefits against microbial resistance risk 2

Common Pitfalls to Avoid

• Using bag specimens for culture—70% specificity results in 85% false-positive rate 2
• Delaying antibiotic treatment—increases risk of renal damage 1, 2
• Treating for <7 days for febrile UTI—inferior outcomes 1, 2
• Using nitrofurantoin for febrile UTI—inadequate tissue penetration 2, 7
• Failing to obtain culture before antibiotics—only opportunity for definitive diagnosis 2, 3
• Treating asymptomatic bacteriuria—requires both positive culture and symptoms 3, 7
• Ordering VCUG routinely after first UTI—not indicated unless specific criteria met 1, 2
• Ordering DMSA scan immediately post-treatment—defer until 4-6 months later 2

When to Refer

• Infants <2-3 months with suspected UTI 3
• Abnormal RBUS showing hydronephrosis, scarring, or structural abnormalities 2
• Recurrent febrile UTIs (≥2 episodes) 2, 3
• Poor response to appropriate antibiotics within 48 hours 2, 3
• Non-E. coli organisms or suspected complicated infection 2

Long-Term Outcomes

• Approximately 15% of children develop renal scarring after first UTI 2
• Renal scarring accounts for ~5% of childhood hypertension and ~3.5% of pediatric end-stage renal disease 2
• Many lesions previously labeled "scars" are congenital dysplasia identified prenatally 2