Urinary tract infection (UTI) ranks among the most common bacterial infections in childhood. UTIs can affect the upper urinary tract (known as pyelonephritis), the lower urinary tract (cystitis), or be present without symptoms (asymptomatic bacteriuria) 1. One of the challenges clinicians face is that distinguishing pyelonephritis from cystitis based on symptoms alone can be genuinely difficult, particularly in infants and young children who cannot describe what they are feeling.

This article covers the key questions parents and healthcare providers commonly ask:

How common is UTI in infants and children?
What symptoms should raise concern?
How do children develop UTI?
How is UTI diagnosed?
When is imaging of the kidneys and bladder appropriate?
How should childhood UTI be managed?

How Common is UTI in Infants and Children?

During the first year of life, roughly 0.7% of girls and 2.7% of uncircumcised boys will develop a UTI. In febrile infants during the first two months, the figures rise to about 5% in girls and 20% in uncircumcised boys. Uncircumcised boys under six months have a 10 to 12-fold increased risk compared to circumcised boys 2.

UTI shows a bimodal pattern, peaking in the first year of life and again between two and four years of age—the toilet training period. By age seven, an estimated 7.8% of girls and 1.7% of boys will have experienced at least one UTI. By sixteen, these figures rise to 11.3% and 3.6% respectively.

After the first year, girls become much more likely than boys to develop UTIs, largely due to anatomical differences (the shorter female urethra).

Recognising UTI Symptoms by Age

Neonates (First Month of Life)

Newborns with UTI rarely present with obvious urinary symptoms. Instead, the infection often mimics generalised illness. A neonate might show:

Temperature instability (either fever or low temperature)
Lethargy or irritability
Poor feeding or weak sucking
Vomiting
Failure to gain weight appropriately
Prolonged jaundice
Apnoea (pauses in breathing)
Signs of sepsis in severe cases

Foul-smelling urine is an uncommon but more specific clue. In neonates with UTI, there is a higher probability of bacteria also being present in the bloodstream, suggesting the infection may have spread from another site.

Infants (1–24 Months)

Throughout infancy, symptoms remain largely non-specific. Unexplained fever is the most common presentation during the first two years—and may be the only symptom. Infants with temperatures above 39°C are more likely to have UTI than those with lower fevers 3.

Other signs to watch for:

Irritability or unusual fussiness
Poor feeding
Vomiting
Recurrent abdominal discomfort
Changes in the number of wet nappies (either more or fewer than usual)
A weak or dribbling urinary stream (which may suggest neurogenic bladder or obstruction)
Constant dribbling or persistent dampness (which could indicate an anatomical abnormality)

Children Over Two Years

After the second year, symptoms become more recognisable. Upper tract infection (pyelonephritis) typically causes:

High fever with chills
Vomiting and general malaise
Flank pain, back pain, or tenderness over the kidney area

Lower tract symptoms (cystitis) include:

Suprapubic pain or abdominal discomfort
Dysuria (pain or burning with urination)
Frequent urination
Urgency
Cloudy or smelly urine
New-onset daytime wetting or bedwetting

What Causes UTI in Children?

Common Pathogens

Escherichia coli causes 80–90% of UTIs in children. Other organisms include:

Klebsiella pneumoniae
Proteus mirabilis (more common in boys)
Enterobacter species
Pseudomonas aeruginosa
Enterococcus species
Staphylococcus saprophyticus (common in sexually active adolescent girls, accounting for about 15% of UTIs in this group)

In children with urinary tract abnormalities or weakened immune systems, a broader range of bacteria may be responsible.

Viruses (particularly adenoviruses) can cause haemorrhagic cystitis—a form of bladder infection with bloody urine. Fungal infections are rare and typically occur in children with indwelling catheters, prolonged antibiotic use, or immune compromise.

Risk Factors

Several factors increase a child’s susceptibility to UTI:

Congenital abnormalities of the kidney and urinary tract (CAKUT), including vesicoureteral reflux
Bladder dysfunction or incomplete emptying
Constipation (quite common and often overlooked)
Not being breastfed
Uncircumcised male infants
Voiding postponement (holding urine too long)
Poor hygiene practices
Sexual activity in adolescents

How Bacteria Reach the Urinary Tract

In most cases (over 90%), bacteria ascend from the periurethral area, travelling up the urethra to the bladder and potentially to the kidneys. The shorter female urethra explains why girls are more susceptible after infancy.

Less commonly, bacteria can spread through the bloodstream (more likely in very young infants) or be introduced through catheterisation.

The body has natural defences: the bladder lining produces protective mucus and antimicrobial substances, and regular voiding flushes bacteria away. When these defences fail—due to incomplete bladder emptying, reflux, or obstruction—infection becomes more likely.

Collecting Urine Samples in Children

Getting a clean urine sample from a baby or young child is genuinely challenging, but proper collection is essential for accurate diagnosis 4.

Collection Methods

Suprapubic aspiration: A needle is inserted through the lower abdominal wall directly into the bladder. Though it sounds invasive, this provides the cleanest sample and is particularly useful in very unwell infants. Ultrasound guidance improves success rates. Complications are rare (occasional brief blood in urine).

Catheterisation: A small tube is passed through the urethra into the bladder. While effective, it causes discomfort and has a small risk of introducing infection.

Clean-catch sample: After cleaning the genital area, urine is caught mid-stream or when the child spontaneously voids. The “Quick-Wee” method—rubbing the suprapubic area with cold saline-soaked gauze—can help trigger voiding in infants 5.

Bag specimens: Adhesive collection bags are convenient but have high contamination rates and should only be used for screening, not diagnosis.

What the Guidelines Say

There is no universal consensus on the best approach. The American Academy of Pediatrics recommends catheterisation or suprapubic aspiration for diagnosis. NICE (UK) guidelines prefer clean-catch methods, reserving invasive collection for severely unwell children. The Canadian Paediatric Society suggests starting with clean-catch and proceeding to catheterisation if initial results are abnormal.

Once collected, urine should be examined promptly. Bacteria double in number every 30 minutes at room temperature—if testing cannot happen immediately, refrigeration at 4°C preserves accuracy for up to four hours.

Diagnosing UTI

Dipstick Tests

Dipstick testing is quick, cheap, and widely available. It detects:

Leucocyte esterase: Indicates white blood cells (suggesting inflammation). Sensitivity around 83%, specificity 78%.
Nitrite: Produced when certain bacteria convert dietary nitrate. Very specific (98%) but less sensitive (53%)—a negative result does not rule out infection, particularly if the child voids frequently or the infecting organism does not produce nitrite.

A positive dipstick warrants further testing but is not diagnostic on its own.

Microscopy

Examining urine under the microscope can reveal bacteria and white blood cells (pyuria). Five or more white blood cells per high-power field in centrifuged urine suggests infection. However, pyuria can occur in other conditions (Kawasaki disease, appendicitis, glomerulonephritis), and its absence on a single specimen does not exclude UTI.

Urine Culture

Urine culture remains the gold standard for diagnosis 6. Results typically take 24–48 hours. What constitutes a “positive” culture depends on how the sample was collected:

Collection Method	Colony Count	Interpretation
Suprapubic aspiration	Any growth (Gram-negative) or >1,000 (Gram-positive)	UTI highly likely
Catheterisation	>50,000 CFU/mL	UTI confirmed
Clean-catch	>100,000 CFU/mL	UTI probable

Mixed growth of multiple organisms usually indicates contamination rather than true infection.

When Is Imaging Needed?

Imaging helps identify children at risk of kidney damage or recurrent infections. However, unnecessary imaging exposes children to radiation and anxiety, so it should be targeted appropriately 7.

Renal and Bladder Ultrasound

Ultrasound is non-invasive, radiation-free, and the first-line imaging study. It can identify:

Kidney size, shape, and position
Hydronephrosis (swelling due to urine backup)
Structural abnormalities
Signs of obstruction
Kidney or perirenal abscesses

Consider ultrasound for:

Children under two with febrile UTI
Any child with recurrent UTI
Children who do not respond to antibiotics within 48 hours
Those with abnormal voiding, hypertension, or palpable abdominal mass

For acutely unwell children, perform ultrasound urgently to rule out obstruction or abscess. Otherwise, waiting 1–2 weeks reduces false positives from temporary inflammation.

DMSA Renal Scan

This nuclear medicine scan detects kidney scarring and acute pyelonephritis. NICE guidelines recommend it 4–6 months after atypical UTI in children under three, or after recurrent UTI at any age. It involves radiation exposure and cost, so routine use is not recommended.

Voiding Cystourethrogram (VCUG)

This X-ray study detects vesicoureteral reflux (urine flowing backward from bladder to kidneys) and other structural abnormalities. It involves catheterisation and radiation.

VCUG is not needed after a first simple UTI if ultrasound is normal. Consider it for:

Recurrent febrile UTI (two or more episodes)
Abnormal ultrasound findings
UTI caused by unusual organisms (not E. coli) combined with high fever

About 25–30% of children with UTI have vesicoureteral reflux, but most cases resolve spontaneously and only a minority require treatment.

Complications and Long-term Risks

Kidney Scarring

Renal scarring develops in up to 5% of girls and 13% of boys after their first pyelonephritis episode. The first two years of life are the most vulnerable period, with risk decreasing after age eight.

Risk factors for scarring include:

High fever (>39°C)
Delay in starting antibiotics
High-grade vesicoureteral reflux
Recurrent episodes

Approximately 10% of children with kidney scars develop hypertension later in life. Women with scars face increased risk of complications during pregnancy. Severe or bilateral scarring can lead to chronic kidney disease.

Other Complications

In the era of effective antibiotics, serious complications like kidney abscess or emphysematous pyelonephritis are rare but can occur in delayed or inadequately treated cases, or in children with underlying abnormalities.

UTI in infancy is also associated with recurrent abdominal pain in later childhood—another reason prompt treatment matters.

Treatment and Prevention

Antibiotic Treatment

Prompt antibiotic therapy should begin once UTI is suspected based on symptoms and urinalysis, without waiting for culture results. The chosen antibiotic should:

Cover common Gram-negative bacteria (especially E. coli)
Achieve high concentrations in urine
Have minimal impact on gut flora
Have low resistance rates in the community

For uncomplicated lower UTI in older children, oral antibiotics for 3–7 days are typically sufficient. Febrile UTI, particularly in infants, may require longer courses or initial intravenous treatment.

Prevention Strategies

Parents can help reduce UTI risk by encouraging:

Regular voiding every 1.5–2 hours (children should not hold urine until the last minute)
Complete bladder emptying with good posture
Adequate fluid intake
Good genital hygiene (wiping front to back in girls)
Treating constipation promptly

For children with recurrent UTIs, particularly those with vesicoureteral reflux, long-term low-dose antibiotic prophylaxis may be considered, though this remains an area of ongoing debate among specialists.

Summary

UTI in infants and children requires a high index of suspicion because symptoms—particularly in young children—are often non-specific. Unexplained fever in infants always warrants consideration of UTI. Proper urine collection is essential for accurate diagnosis, and urine culture remains the gold standard.

Most children with UTI recover fully with appropriate antibiotic treatment. Imaging should be targeted at those at risk of complications rather than performed routinely. Addressing predisposing factors like constipation and voiding habits can help prevent recurrence.

If your child has symptoms suggestive of UTI, particularly fever without an obvious source, seek medical evaluation promptly. Early treatment reduces the risk of kidney damage and other complications.

References

Mattoo TK, Shaikh N, Nelson CP. Contemporary Management of Urinary Tract Infection in Children. Pediatrics. 2021;147(2):e2020012138. PubMed
Shaikh N, Morone NE, Bost JE, Farrell MH. Prevalence of urinary tract infection in childhood: a meta-analysis. Pediatr Infect Dis J. 2008;27(4):302-308. PubMed
National Institute for Health and Care Excellence (NICE). Urinary tract infection in under 16s: diagnosis and management. NICE guideline NG224. 2022. NICE
Williams GJ, Macaskill P, Chan SF, et al. Absolute and relative accuracy of rapid urine tests for urinary tract infection in children: a meta-analysis. Lancet Infect Dis. 2010;10(4):240-250. PubMed
Kaufman J, Fitzpatrick P, Tosif S, et al. Faster clean catch urine collection (Quick-Wee method) from infants: randomised controlled trial. BMJ. 2017;357:j1341. PubMed
Subcommittee on Urinary Tract Infection. Reaffirmation of AAP Clinical Practice Guideline: The Diagnosis and Management of the Initial Urinary Tract Infection in Febrile Infants and Young Children 2-24 Months of Age. Pediatrics. 2016;138(6):e20163026. PubMed
Hoberman A, Charron M, Hickey RW, et al. Imaging studies after a first febrile urinary tract infection in young children. N Engl J Med. 2003;348(3):195-202. PubMed