OVERVIEW

What is pediatric urinary tract infection?

Urinary tract infection (UTI) refers to the invasion of pathogens directly into the urinary tract, where they grow and multiply in the urine, damaging the mucosa and tissues of the urinary tract. Depending on the site of infection, UTIs are generally classified as pyelonephritis, cystitis, or urethritis. Pyelonephritis is also known as upper urinary tract infection, while cystitis and urethritis are collectively referred to as lower urinary tract infections.

In children, infections are rarely confined to a single part of the urinary tract, and clinical localization is often difficult. Therefore, they are commonly referred to collectively as "urinary tract infections" (UTIs). Clinically, UTIs in children can be categorized as "symptomatic urinary tract infections" or "asymptomatic bacteriuria" based on the presence or absence of symptoms.

At what age is pediatric UTI most common?

In China, the annual incidence of symptomatic UTIs in children is 1.7–3.8 per 1,000 in boys and 3.1–7.1 per 1,000 in girls, with the peak incidence occurring between 2 and 5 years of age. Asymptomatic bacteriuria is more common in school-aged girls.

Several large international studies have shown that the overall prevalence of UTIs in febrile infants and young children is about 7%, though this varies by age, race/ethnicity, sex, and circumcision status. Among white girls with a fever of ≥39°C, the prevalence of UTI is 16%.

What is the prognosis (recovery) for pediatric UTI?

With appropriate antibiotic treatment, most acute UTIs resolve within days, and symptoms disappear. However, nearly 50% of patients may experience recurrence, and about 25% of children develop vesicoureteral reflux (VUR).

Recurrent cases are often associated with urinary tract abnormalities, with VUR being the most common. VUR is closely related to renal scarring, which is the most critical factor affecting the prognosis of pediatric UTIs.

Renal scarring is most likely to form in school-aged children, with little progression after age 10. If hypertension caused by renal scarring is not effectively controlled, it can eventually lead to chronic renal failure.

SYMPTOMS

What are the symptoms of urinary tract infections in children?

Acute urinary tract infection (UTI):

Symptoms vary significantly depending on the child's age. Infants and young children often present with nonspecific (atypical) clinical symptoms, requiring special attention.

• Newborns: Symptoms are highly atypical, primarily systemic, such as fever or hypothermia, pale skin, poor feeding, vomiting, diarrhea, jaundice, etc. Some may exhibit neurological symptoms like lethargy, irritability, or even seizures. Neonatal UTIs are often accompanied by sepsis, but urinary symptoms (frequency, urgency, pain) are usually absent. About 30% of cases show the same pathogen in blood and urine cultures.
• Infants and toddlers:
  • Especially under 2 years old, symptoms are often nonspecific, with fever being the most prominent. Other systemic signs include refusal to eat, vomiting, and diarrhea. Jaundice or neurological symptoms (e.g., lethargy, drowsiness, irritability, seizures) may also occur.
  • Infants <3 months may show fussiness, drowsiness, feeding difficulties, or developmental delays.
  • Older infants (>3 months) and children may exhibit urinary frequency, dysuria, hematuria, pyuria, or cloudy urine. Nonverbal infants may display fussiness during urination, foul-smelling diapers, or persistent diaper rash.
• Older children: Systemic symptoms like fever, chills, or abdominal pain dominate. They may report lower abdominal or flank pain. Physical exam may reveal costovertebral angle tenderness or kidney percussion pain. Urinary symptoms (frequency, urgency, dysuria, cloudy urine) are pronounced, with occasional gross hematuria.

Chronic urinary tract infection:

• Defined as persistent or recurrent infections lasting >1 year, often accompanied by anemia, weight loss, growth delay, hypertension, or renal dysfunction.

Asymptomatic bacteriuria:

• Detected via routine urinalysis in healthy children (positive urine culture) without UTI symptoms. Common in school-aged girls. Often associated with urinary tract abnormalities or prior symptomatic UTIs, with E. coli being the predominant pathogen.

CAUSES

What causes urinary tract infections in children?

Any pathogenic bacteria can cause urinary tract infections, but the vast majority are Gram-negative bacilli, such as Escherichia coli, Paracolobactrum, other Enterobacteriaceae, Proteus, Citrobacter, Klebsiella, and Pseudomonas aeruginosa. A small number are caused by Enterococcus and Staphylococcus.

Escherichia coli is the most common pathogen in urinary tract infections, accounting for about 60%–80%. If the infection is caused by microorganisms other than Escherichia coli, it is more likely to be associated with renal scarring.

For newborns with their first urinary tract infection, girls of all ages, and boys under 1 year old, the main pathogen is still Escherichia coli. In boys over 1 year old, Proteus is the predominant pathogen. For girls aged 10–16, Staphylococcus albus is also common. Klebsiella and Enterococcus are more frequently seen in neonatal urinary tract infections.

How do urinary tract infections occur in children?

The pathogenesis of bacterial urinary tract infections is complex, primarily resulting from the interaction between host intrinsic factors and bacterial pathogenicity.
Routes of infection:

• Ascending infection: This is the most common route of urinary tract infection. Pathogens ascend from the urethral opening into the bladder, causing cystitis. The bacteria in the bladder then migrate to the kidneys via the ureters, leading to pyelonephritis. The main pathogens causing ascending infections are Escherichia coli, followed by Proteus or other Enterobacteriaceae.
• Hematogenous infection: Pathogens such as Staphylococcus aureus can invade the urinary tract through the bloodstream (sepsis or bacteremia).
• Lymphatic spread and direct extension: Bacteria from the colon or pelvis can infect the kidneys via lymphatic vessels, and infections in adjacent organs or tissues can also spread directly.

Host intrinsic factors:

• Changes in periurethral bacterial flora and urine properties create conditions for pathogen invasion and proliferation.
• Bacterial adhesion to urothelial cells (colonization) is a prerequisite for their proliferation and subsequent urinary tract infection.
• Patients with urinary tract infections often have defective secretory IgA production, leading to reduced urinary secretory IgA levels and increased susceptibility to infection.
• Congenital or acquired urinary tract abnormalities increase the risk of urinary tract infections.
• Newborns and infants have weaker immune defenses, making them more prone to urinary tract infections. Diapers and the urethral opening are often contaminated with bacteria, and local defense mechanisms are underdeveloped, facilitating ascending infections.
• Children with diabetes, hypercalcemia, hypertension, chronic kidney disease, sickle cell anemia, or those on long-term corticosteroid or immunosuppressive therapy have a higher incidence of urinary tract infections.

Under what circumstances can urinary tract infections in children lead to renal scarring?

Renal scarring refers to the loss of renal parenchyma between the renal calyx and the renal capsule, which is a potential complication of urinary tract infections. Long-term consequences of renal scarring may include hypertension, reduced renal function, proteinuria, and end-stage renal disease. The following factors have been confirmed to be associated with renal scarring:

• Recurrent febrile urinary tract infections.
• Delayed treatment of acute infection (fever lasting more than 72 hours).
• Bladder and bowel dysfunction (manifested as daytime enuresis, urinary incontinence, and constipation).
• Obstructive urinary tract abnormalities.
• Vesicoureteral reflux (VUR).

DIAGNOSIS

How is pediatric urinary tract infection diagnosed?

Quantitative urine culture is the standard test for diagnosing urinary tract infections (UTIs). The optimal diagnostic criteria for UTIs are defined as the presence of significant bacteriuria (positive urine culture) in patients with pyuria (positive leukocyte count or white blood cells in urinalysis).

However, there are exceptions:

• For children with UTI symptoms, a diagnosis may still be made in the absence of pyuria if the urine culture confirms significant growth of Enterococcus, Klebsiella, or Pseudomonas aeruginosa.
• Some children with UTIs caused by Escherichia coli may not exhibit pyuria (the accuracy of positive leukocyte detection in urinalysis is up to 90%). Therefore, clinical judgment or repeat urinalysis and urine culture are necessary to rule out specimen contamination if a urinary pathogen is detected without pyuria.
• Older children with UTIs present symptoms similar to adults, such as obvious urinary irritation, which is often the chief complaint. A confirmed diagnosis can be made immediately if combined with positive laboratory results.
• However, in infants and young children, especially newborns, urinary irritation symptoms may be absent or subtle, while systemic manifestations are more prominent, leading to missed diagnoses. Thus, for children with unexplained fever, repeated urine tests should be performed, and urine culture colony counts and antibiotic sensitivity tests should ideally be conducted before antibiotic treatment. The presence of significant bacteriuria confirms the diagnosis.

What constitutes significant bacteriuria in pediatric UTIs?

Significant bacteriuria depends on the method of urine collection (clean-catch midstream sample, catheterized sample, or suprapubic bladder aspiration sample) and the identification of isolated pathogens.

Generally, Lactobacillus, coagulase-negative staphylococci, and Corynebacterium are not considered clinically significant urinary pathogens.

Under what circumstances can urine culture yield false-negative results in pediatric UTIs?

False-negative results may occur in the following situations:

• Presence of antibiotics in the urine that inhibit bacterial growth.
• Rapid urine flow reducing bacterial multiplication time.
• Ureteral obstruction preventing bacteria from entering the bladder.
  Therefore, for children with asymptomatic or unexplained fever, urine tests should be performed before antibiotic treatment, and repeated testing may be necessary. If urine culture results are inconclusive, renal cortical scintigraphy (^99mTc-DMSA) may help confirm acute pyelonephritis.

What tests should be performed for pediatric UTIs?

A comprehensive UTI diagnosis should include not only confirmation of bacterial infection but also the following assessments:

• Determining whether the infection is a first episode, recurrence, or reinfection.
• Identifying the pathogen type and conducting antibiotic sensitivity testing.
• Evaluating for urinary tract abnormalities, such as vesicoureteral reflux (VUR) or obstruction. If VUR is present, further assessment of its severity and the presence of renal scarring is needed.
• Localizing the infection (upper or lower urinary tract).

The following tests are recommended:

• Urinalysis/urine leukocyte count + urine culture. Routine and possibly repeated testing is required.
• Ultrasound. A non-invasive test that can reveal kidney size and morphology, ureteral duplication, hydroureter, and obvious anatomical abnormalities. Ultrasound is recommended for:
  • Children under 2 years with febrile first-time UTIs.
  • Children of any age with recurrent febrile UTIs.
  • Children with a family history of kidney or urinary tract disease, growth delay, or hypertension.
  • Children with UTIs who do not respond adequately to antibiotic therapy.
• Voiding cystourethrogram (VCUG/MCU). VCUG is the preferred test to diagnose VUR and assess its severity. It is recommended for:
  • Children of any age with ≥2 febrile UTIs.
  • Children of any age with a first febrile UTI if renal ultrasound shows abnormalities, fever ≥39°C with a non-E. coli pathogen, or growth delay/hypertension.
• Renal cortical scintigraphy (^99mTc-DMSA). Detects acute pyelonephritis, renal scarring, and split renal function in acute and chronic phases. Some experts recommend DMSA as the initial imaging for high-risk children (top-down approach).
  • NICE guidelines recommend DMSA 4–6 months post-infection for children under 3 with atypical/recurrent UTIs and children over 3 with recurrent UTIs.
  • Atypical cases include severe illness, poor urine flow, abdominal/bladder mass, elevated creatinine, sepsis, non-E. coli infections, or no response to antibiotics within 48 hours.
  • Recurrent UTIs: ≥2 upper UTIs, 1 upper UTI + ≥1 lower UTI, or ≥3 lower UTIs.
  • Current evidence does not support routine DMSA for first-time UTIs.

What conditions should pediatric UTIs be differentiated from?

• UTIs must be distinguished from glomerulonephritis, renal tuberculosis, and acute urethral syndrome. Acute urethral syndrome presents with urinary irritation symptoms (frequency, urgency, dysuria) but has no bacterial growth or insignificant bacteriuria in clean-catch urine culture.
• Urinary symptoms (e.g., urgency, frequency, dysuria) and bacteriuria may also result from: nonspecific vulvovaginitis, irritant/chemical urethritis (e.g., bubble baths), urinary stones, sexually transmitted infections (especially chlamydia), or vaginal foreign bodies. These can be excluded based on UTI definitions and exceptions.
• Group A streptococcal infections, appendicitis, and Kawasaki disease may also cause fever, abdominal pain, and pyuria, but urine cultures are negative.

TREATMENT

Which department should I visit for pediatric urinary tract infection?

Pediatrics, Pediatric Nephrology.

Does pediatric urinary tract infection require hospitalization?

Most infants and children over 2–3 months of age with uncomplicated urinary tract infections can be treated as outpatients and undergo relevant tests.

Hospitalization is required if outpatient treatment is ineffective, or if the child is very young, has complex symptoms, severe infection, urinary tract abnormalities, poor immune function, cannot take oral medication, or lacks access to timely follow-up.

How is pediatric urinary tract infection treated?

Acute urinary tract infection:

In addition to relieving symptoms, it is necessary to prevent recurrence, reduce and prevent long-term complications such as hypertension, renal scarring, impaired kidney growth, and functional damage. Early antibiotic treatment (especially within 72 hours of symptom onset) is crucial to avoid kidney damage.

For children suspected of having a urinary tract infection with positive urine white blood cells or leukocyte counts, empirical antibiotic therapy should begin after proper urine sample collection for culture.

• Anti-infection: Second-generation cephalosporins or amoxicillin-clavulanate are recommended.
  • Outpatient oral options include cefixime, cefdinir, and cefpodoxime.
  • Hospital intravenous options include cefotaxime, ceftriaxone, and cefepime.
  • Adjust treatment based on efficacy and urine culture sensitivity results.
• Treatment duration:
  • If upper or lower urinary tract infection is identified, use a long course (10–14 days) for upper tract infections, and a standard (7–14 days) or short course (2–4 days) for lower tract infections.
  • Since differentiating upper and lower tract infections is difficult in infants, a longer course (10–14 days) is recommended for febrile cases, while a short course (3–5 days) is suitable for afebrile children with normal immune function.

Recurrent urinary tract infection:

• For recurrent cases, investigate underlying conditions such as vesicoureteral reflux, urinary tract malformations, stones, or bladder/bowel dysfunction, and collaborate with urology specialists.
• For children without vesicoureteral reflux but with ≥3 febrile UTIs in 6 months or ≥4 UTIs in a year, dual-antibiotic long-term therapy may be needed, possibly including prophylactic antibiotics for 6 months.

Asymptomatic bacteriuria:

• Generally, no treatment is required as most cases resolve spontaneously without causing kidney scarring, impaired function, or growth issues.
• However, if accompanied by urinary obstruction, reflux, malformations, or prior kidney scarring, aggressive antibiotic therapy followed by low-dose prophylaxis until the abnormality is corrected is recommended.

Is a follow-up urine test needed after treatment for pediatric urinary tract infection?

It depends.

• Evaluate treatment efficacy 48 hours after antibiotics, including symptoms and urine tests. If the pathogen is identified and sensitive antibiotics are used, repeat urine culture is usually unnecessary.
• If the expected improvement is not seen after 48 hours, repeat urine culture is required.

DIET & LIFESTYLE

What should be paid attention to in daily life for pediatric urinary tract infections?

• Maintain a normal and balanced diet with a variety of foods to ensure adequate nutrition during illness;

• Ensure sufficient fluid intake to maintain normal urine output;

• Get enough rest and adequate sleep daily to aid recovery.

• Pay attention to local hygiene and cleanliness.

PREVENTION

How to prevent urinary tract infections in children?

• Maintain personal hygiene and avoid wearing overly tight underwear;

• Change diapers promptly and clean the genital area frequently to prevent bacterial invasion;

• Detect and address conditions such as phimosis in boys or labial fusion and pinworm infections in girls promptly;

• Correct urinary tract abnormalities early to prevent urinary obstruction and kidney scarring;

• Use antibiotics properly and avoid unnecessary antibiotic use for respiratory or digestive infections.