# Pediatric Urinary Tract Infections

## Overview

UTI is the most common serious bacterial infection in febrile infants and young children. Prevalence varies by age, sex, and circumcision status, affecting approximately 5% of febrile infants, with higher rates in uncircumcised males under 3 months and females over 12 months. Accurate diagnosis requires a properly collected urine specimen, which is non-negotiable. The goals of management are to treat the acute infection, identify urinary tract abnormalities that predispose to recurrence, and prevent renal scarring.

## Epidemiology

In infants under 3 months, males are affected more than females, with uncircumcised males having a roughly 10-fold higher risk. After 12 months, females are affected far more often due to the short urethra and proximity to the perineum. Circumcision reduces UTI risk by approximately 90% in the first year of life. The most common pathogens are E. coli (about 80%), Klebsiella, Proteus (more common in boys and associated with struvite stone formation), Enterobacter, Enterococcus, and Pseudomonas (which should be considered in complicated or recurrent UTIs).

## Diagnosis

### Urine Collection Methods

A catheterized specimen is the preferred method in non-toilet-trained children and is clean and reliable. Suprapubic aspiration (SPA) is the gold standard, especially in neonates, where any growth is significant. Clean-catch midstream collection is acceptable in toilet-trained children. Bag specimens have a high contamination rate (over 50% false positive) and are acceptable only for screening. A negative bag urine can rule out UTI, but a positive bag urine cannot diagnose UTI and must be confirmed with a catheterized specimen.

### Urinalysis Interpretation

Leukocyte esterase is sensitive but not specific and can be positive in non-UTI conditions such as irritation, fever, or dehydration. Nitrites are highly specific for gram-negative bacteria (E. coli converts nitrate to nitrite) but have low sensitivity (about 50%) because urine must remain in the bladder for at least 4 hours. Pyuria is defined as 5 or more WBC/HPF on standard UA or 10 or more WBC/mm3 on hemocytometer or enhanced UA. Bacteria on Gram stain of unspun urine is highly predictive when present. The AAP diagnostic criteria require both pyuria and bacteriuria on enhanced UA along with a positive culture.

### Urine Culture

| Collection Method | Positive Culture Threshold | Notes |
|------------------|--------------------------|-------|
| Suprapubic aspiration | Any gram-negative growth; ≥1,000 CFU/mL gram-positive | Gold standard in neonates |
| Catheterized | ≥50,000 CFU/mL (some use ≥10,000) | Preferred in non-toilet-trained |
| Clean-catch midstream | ≥100,000 CFU/mL | Toilet-trained children |
| Bag specimen | Not diagnostic (>50% false positive) | Negative result can rule out UTI |

A urine culture provides definitive diagnosis. Positive culture thresholds depend on collection method: catheterized specimens require 50,000 CFU/mL or greater of a single pathogen (some use 10,000 or greater), SPA requires any growth of gram-negative organisms or 1,000 CFU/mL or greater of gram-positive organisms, and clean-catch requires 100,000 CFU/mL or greater of a single pathogen. Mixed flora or low colony counts suggest contamination.

<image>Diagnostic algorithm for pediatric UTI showing urine collection method by age and toilet-training status (bag for screening only, catheterization or SPA for definitive specimen), urinalysis interpretation (leukocyte esterase, nitrites, microscopy), and urine culture thresholds for each collection method</image>

## Treatment

### Acute Management

Outpatient treatment is appropriate for uncomplicated UTI in well-appearing children who can tolerate oral intake. Oral antibiotics are given for 7-14 days (AAP recommends 7-14 days, with recent data supporting 7 days). First-line agents include cephalexin, cefixime, amoxicillin-clavulanate, and TMP-SMX (if susceptible), with adjustment based on culture and sensitivity results. Inpatient treatment is indicated for complicated UTI, ill-appearing infants, those unable to tolerate oral intake, and neonates. IV antibiotics include ceftriaxone (50-75 mg/kg/day) or ampicillin plus gentamicin (for neonates), with step-down to oral antibiotics when the patient is improving and tolerating oral intake, for a total duration of 7-14 days. Neonates always require IV treatment, a full sepsis workup including LP, and admission.

### Follow-Up

Clinical improvement is expected within 48 hours. If not improving, a resistant organism, abscess, or obstruction should be considered. Repeat urine culture during treatment is not routinely recommended if clinical improvement occurs, nor is a repeat culture at the end of treatment routinely needed.

## Imaging

### Renal and Bladder Ultrasound (RBUS)

The AAP recommends RBUS for all children 2-24 months with a first febrile UTI. It evaluates for hydronephrosis, renal size discrepancy, bladder wall thickening, renal abscess, and structural anomalies. RBUS does not reliably detect vesicoureteral reflux (VUR), which requires a VCUG. Timing is within 48 hours if the child is ill-appearing or not responding, otherwise within 2-4 weeks.

### Voiding Cystourethrogram (VCUG)

VCUG is the gold standard for detecting and grading VUR. The AAP does not recommend VCUG after a first febrile UTI if RBUS is normal. Indications for VCUG include abnormal RBUS (hydronephrosis, renal scarring, ureteral dilation), recurrent febrile UTIs (2 or more episodes), atypical or complex UTI (not responding to treatment, unusual organism), and family history of high-grade VUR. VUR is graded I through V: grades I-II are low-grade with a high spontaneous resolution rate, grade III is moderate, and grades IV-V are high-grade with a higher risk of scarring and greater likelihood of requiring intervention.

### DMSA Renal Scan

The DMSA nuclear medicine scan is the best test for detecting acute pyelonephritis and renal scarring. It is not routinely performed for a first UTI but is useful in recurrent UTIs or when assessing for renal scarring to guide management decisions.

<image>Imaging approach after pediatric febrile UTI showing RBUS for all children 2-24 months with first febrile UTI, VCUG indications (abnormal RBUS, recurrent febrile UTI, atypical presentation), VUR grading system (grades I-V with diagrams), and DMSA scan for renal scarring assessment when indicated</image>

## Vesicoureteral Reflux (VUR)

### Pathophysiology

VUR results from an incompetent vesicoureteral junction that allows retrograde urine flow from the bladder to the ureter and kidney. Primary VUR is a congenital short intramural ureter that is often familial. Secondary VUR arises from bladder dysfunction, posterior urethral valves, or neurogenic bladder.

### Natural History

Low-grade VUR (grades I-II) resolves spontaneously in approximately 80% by age 5-6 years. High-grade VUR (grades IV-V) resolves in only 20-30% and carries a higher risk of recurrent UTI and renal scarring.

### Management

#### Antibiotic Prophylaxis

The RIVUR trial (2014) demonstrated that continuous antibiotic prophylaxis (TMP-SMX) reduced UTI recurrence by approximately 50% in children with grades I-IV VUR. However, prophylaxis did not reduce renal scarring and increased antibiotic-resistant infections. Current practice is to consider prophylaxis selectively for high-grade VUR (grades III-V), breakthrough UTIs, and younger children. Commonly used agents are TMP-SMX or nitrofurantoin at one-third to one-quarter of the treatment dose.

#### Surgical Options

Endoscopic injection (dextranomer/hyaluronic acid, known as Deflux) is an outpatient procedure with 70-80% success for grades II-IV. Ureteral reimplantation (open or robotic) has a greater than 95% success rate and is definitive. Indications for surgery include breakthrough UTIs on prophylaxis, high-grade VUR not resolving, and parental preference.

## Bladder and Bowel Dysfunction (BBD)

BBD often coexists with VUR and recurrent UTIs. Symptoms include urgency, frequency, holding maneuvers, constipation, and encopresis. Constipation management is essential because a full rectum compresses the bladder and impairs emptying. Behavioral therapy includes timed voiding every 2-3 hours, adequate fluid intake, and aggressive constipation treatment. Treating BBD reduces UTI recurrence and improves VUR resolution rates.

## Clinical Pearls

A bag urine specimen cannot diagnose UTI; if positive, it must always be confirmed with a catheterized or SPA specimen. Circumcision is protective against UTI in the first year of life, which is relevant counseling for parents of newborn males. If a febrile infant is not improving after 48 hours of appropriate antibiotics, imaging should be obtained and alternative diagnoses considered (renal abscess, resistant organism, obstruction). Bladder and bowel dysfunction should always be assessed in children with recurrent UTIs because treating constipation alone may significantly reduce UTI recurrence. Proteus UTI in boys should prompt evaluation for structural abnormality because Proteus is associated with struvite stone formation. VCUG is not needed after the first febrile UTI if the renal ultrasound is normal, avoiding an invasive and potentially traumatic procedure.

## Key Controversy: Antibiotic Prophylaxis for VUR

The RIVUR trial showed prophylaxis reduces UTI recurrence but not renal scarring. Ongoing concern exists about promoting antibiotic resistance with long-term low-dose prophylaxis. The Swedish Reflux Trial found no difference in renal scarring at 2 years between prophylaxis plus surveillance, surveillance alone, and endoscopic treatment. The current approach is increasingly selective, with prophylaxis reserved for high-grade VUR, young infants, and those with breakthrough UTIs. Some centers advocate for surveillance alone in low-grade VUR with close monitoring. Parent preferences and family circumstances should be incorporated into shared decision-making. Future research into biomarkers for identifying children at highest risk for renal scarring may enable more personalized prophylaxis decisions.

## References
- Subcommittee on Urinary Tract Infection. Reaffirmation of AAP Clinical Practice Guideline: Diagnosis and Management of the Initial UTI in Febrile Infants and Children 2-24 Months. Pediatrics. 2016;138(6):e20163026.
- Hoberman A, et al. Antimicrobial Prophylaxis for Children with Vesicoureteral Reflux (RIVUR). N Engl J Med. 2014;370(25):2367-2376.
- Roberts KB. Urinary Tract Infection: Clinical Practice Guideline for the Diagnosis and Management of the Initial UTI in Febrile Infants and Children 2-24 Months. Pediatrics. 2011;128(3):595-610.
- Brandstrom P, et al. The Swedish Reflux Trial in Children: Long-Term Results. J Urol. 2019;201(6):1192-1199.
- Shaikh N, et al. Identification of Children and Adolescents at Risk for Renal Scarring After a First Urinary Tract Infection. JAMA Pediatr. 2014;168(10):893-900.