Paediatrics chapters
Urinary tract infection in children
How urinary infection presents at different ages, how to collect urine and read the culture, which antibiotics to use, when to image, and how vesicoureteric reflux leads to scarring.
- UTI is usually caused by E. coli ascending from bowel flora; in infants it is commoner in boys (especially uncircumcised), after infancy much commoner in girls.
- Infants show fever, poor feeding, vomiting, jaundice or failure to thrive; from about 2 years classic dysuria, frequency and flank pain appear; diagnosis needs pyuria plus a positive culture from a properly collected sample.
- Treat with oral or IV antibiotics (IV for infants and toxic children), image with ultrasound, and look for vesicoureteric reflux (MCUG) and scars (DMSA) when indicated.
On this page
Overview
Urinary tract infection (UTI) means bacterial infection of the bladder (cystitis), the kidney (pyelonephritis), or rarely a renal abscess. It is common, often hidden in infants, and important because infection of a growing kidney, especially with vesicoureteric reflux (VUR), can leave scars that later cause hypertension and chronic kidney disease. Every febrile infant without an obvious source should have UTI excluded.
Epidemiology
- About 1 to 4 per 1000 premature and newborn infants; many neonatal UTIs are blood-borne.
- Newborns and young infants: commoner in boys, especially uncircumcised boys (5 to 12 times the risk).
- After infancy: much commoner in girls (Akbar: about 10 times); Nelson puts the figure by age 11 at roughly 8% for girls versus 2% for boys.
- Recurrence is frequent: Nelson gives a relapse rate of 25 to 40%, mostly within weeks.
Organisms
| Organism | Notes |
|---|---|
| Escherichia coli | About 75 to 90% of infections; P fimbriae help it stick to urinary lining cells |
| Klebsiella, Proteus, Pseudomonas | Other Gram-negative causes |
| Enterococcus | Gram-positive; covered by ampicillin |
| Staphylococcus saprophyticus | Sexually active adolescent girls |
Nearly all UTIs come from bowel (faecal) organisms ascending the urethra; in the neonate spread may be haematogenous.
Risk factors
- Female sex (short urethra), uncircumcised male infant.
- Vesicoureteric reflux and other anomalies: posterior urethral valves, pelviureteric junction obstruction, hydronephrosis, duplex kidneys.
- Incomplete bladder emptying: neurogenic bladder (spina bifida), constipation, voiding dysfunction.
- Stones, catheters and instrumentation.
- Poor perineal hygiene, wiping back to front, pinworms.
Clinical features by age
| Age | Usual picture |
|---|---|
| Newborn | Fever or hypothermia, poor feeding, vomiting, jaundice (conjugated, from Gram-negative toxin), failure to thrive, sepsis |
| Infant to 2 years | Unexplained fever, vomiting, diarrhoea, irritability, poor weight gain; may mimic gut illness |
| Preschool | Abdominal pain, vomiting, foul-smelling urine, fever, new enuresis, frequency |
| School age and older | Classic dysuria, frequency, urgency, enuresis, fever, flank pain and costovertebral angle tenderness; sometimes haemorrhagic cystitis |
Classic urinary symptoms are unreliable before about 2 years. A febrile infant with no focus needs a urine test.
Upper versus lower UTI
| Feature | Pyelonephritis | Cystitis |
|---|---|---|
| Fever over 39 °C | Common | Very unusual |
| Systemic upset | Common | Very unusual |
| White cell count | Often over 20,000 | Usually normal |
| ESR / CRP | Almost always raised | Unusually raised |
| Dysuria, frequency | Variable | Common |
| Flank pain, CVA tenderness | Common (not in infants) | Absent |
| DMSA scan | Areas of reduced uptake | Normal |
Pyelonephritis is more often linked to bacteraemia and anatomical abnormality, so localisation matters.
Diagnosis
Collecting urine
| Method | Use |
|---|---|
| Clean-catch midstream | Older, toilet-trained children |
| Urethral catheterisation | Infants and young children before starting antibiotics |
| Suprapubic aspiration | Infants; a more specific method, though invasive |
| Sterile bag | Easily contaminated: not suitable for culture; a negative bag test helps, a positive one must be confirmed |
Examine urine within about 20 minutes or refrigerate it.
Urine tests
- Pyuria: Akbar uses more than 5 white cells per high-power field; white cell casts support infection. Pyuria also occurs with fever, dehydration, nephritis or contamination, and up to half of real UTIs may lack pus cells.
- Dipstick: leucocyte esterase plus nitrite together are useful (high specificity); either alone is weak. Nitrite needs time in the bladder and may be negative with frequent voiding.
- Culture is the gold standard.
| Sample | Significant growth (single organism) |
|---|---|
| Clean-catch, older child | 100,000 CFU/mL or more |
| Catheter specimen, infant | 50,000 CFU/mL or more, with pyuria (Nelson) |
Counts can be falsely low if the child is on antibiotics, the urine is very dilute, or antiseptic contaminates the sample.
Treatment
General
- Antipyretics, good fluid intake, correct dehydration and electrolytes.
- Start empirical antibiotics once urine is sent, then adjust to culture and sensitivity and local resistance.
Who needs IV antibiotics and admission
- Neonates and young infants.
- Children who look toxic, are dehydrated, or cannot keep oral fluids down.
- Switch to oral once improving (usually 24 to 48 hours).
Antibiotics (doses as given in Akbar)
| Route | Drug | Dose |
|---|---|---|
| Oral | Amoxicillin | 20 to 50 mg/kg/day, split into 3 doses |
| Oral | Co-amoxiclav | 20 to 45 mg/kg/day, split into 3 doses |
| Oral | Cefixime | 8 mg/kg/day once daily |
| Oral | Cephradine | 50 mg/kg/day, split into 2 to 4 doses |
| Oral | Trimethoprim | 8 mg/kg/day, split into 2 doses |
| Oral | Nitrofurantoin | 3 to 5 mg/kg/day, split into 4 doses |
| Oral | Nalidixic acid | 50 mg/kg/day, split into 4 doses |
| IV | Ceftriaxone | 50 mg/kg/day |
| IV | Gentamicin | 6 mg/kg/day, split into 2 to 3 doses (adjust in renal failure) |
| IV | Ampicillin (for enterococci) | 100 to 200 mg/kg/day, split into 4 doses |
Duration
- Neonates: 10 to 14 days, given parenterally (bacteraemia is common).
- Older children: 7 to 14 days (Nelson); Akbar gives 10 to 14 days for an uncomplicated case with one oral drug.
- If there is no improvement within 48 hours, repeat the culture and image promptly.
Pus cells alone do not prove UTI (they occur with fever, dehydration and nephritis), and their absence does not exclude it. The diagnosis rests on a properly collected culture.
Imaging
| Test | What it shows | When |
|---|---|---|
| Ultrasound kidneys and bladder | Hydronephrosis, obstruction, anomalies, stones; can be repeated to follow kidney growth | All infants with febrile UTI (Nelson); Akbar advises it to look for obstruction or anomalies |
| MCUG (micturating cystourethrogram) | Vesicoureteric reflux and its grade; posterior urethral valves; bladder shape | Abnormal ultrasound, recurrent UTI, suspected reflux or valves |
| DMSA scan | Renal scars (late) and acute pyelonephritis (areas of low uptake) | To define scarring after infection |
| DTPA or MAG3 scan | Drainage and obstruction | Suspected obstruction |
MCUG detects reflux; DMSA detects scars; ultrasound detects structural problems.
Vesicoureteric reflux (VUR)
- Backflow of urine from bladder up the ureter, sometimes into the kidney.
- Primary VUR: a congenitally short or abnormal ureteric entry into the bladder wall (vesicoureteric junction); tends to improve as the child grows. Runs in families (30 to 40% of siblings).
- Secondary VUR: high bladder pressure from posterior urethral valves or neurogenic bladder (up to half have VUR).
- The younger the child with UTI, the likelier reflux is present; it is the commonest abnormality found on imaging after UTI (Nelson).
- Renal scarring is a particular risk when reflux is combined with infection or obstruction: about 15% with low-grade reflux, about 65% with grade IV or V (Nelson); it leads to reflux nephropathy, hypertension and CKD.
International grading
| Grade | Description |
|---|---|
| I | Into a non-dilated ureter only |
| II | Up to pelvis and calyces, no dilatation |
| III | Mild to moderate dilatation, slight blunting of fornices |
| IV | Moderate dilatation and tortuosity, blunted calyces |
| V | Gross dilatation and tortuosity, loss of calyceal pattern |
Grades 1 to 5 go "ureter, kidney, dilate, twist, destroy".
Management of VUR
- Most mild reflux settles with growth; treat UTIs promptly, manage constipation and voiding habits.
- Continuous antibiotic prophylaxis for children with reflux, other anomalies or recurrent UTI (Akbar).
- Surgical or endoscopic correction (e.g. endoscopic injection) for selected high-grade reflux or breakthrough infections; the indications are debated.
Prophylaxis
- Low-dose antibiotic once daily at bedtime: trimethoprim 2 mg/kg or nitrofurantoin 1 mg/kg (Akbar).
- Nelson notes prophylaxis may prevent more severe recurrences, but the effect is small.
- Cranberry juice is not a substitute for proper prevention.
Prevention of recurrence
- Good perineal hygiene, wiping front to back.
- Treat constipation and voiding dysfunction; frequent, complete bladder emptying.
- Adequate fluid intake; treat pinworms.
- Follow-up urine culture when symptoms recur (Akbar suggests periodic cultures for a year).
Complications
- Bacteraemia and sepsis (mainly infants).
- Renal abscess (uncommon).
- Renal scarring and reflux nephropathy → hypertension and chronic kidney disease.
Prognosis
UTI confined to the bladder has an excellent outlook. Once the kidney is involved, especially in infants with reflux or obstruction, the outlook is more guarded.
Expect: E. coli and P fimbriae; boys more in the newborn period and girls after; non-specific presentation in infants (fever, jaundice, failure to thrive); clean-catch and catheter colony counts and why bag samples are not for culture; leucocyte esterase plus nitrite; IV antibiotics for neonates and toxic children, 10 to 14 days in neonates; ultrasound for all febrile infants; MCUG for reflux and posterior urethral valves; DMSA for scars; reflux grades I to V; scarring (commoner with high-grade reflux) leading to hypertension and CKD; and trimethoprim or nitrofurantoin prophylaxis.
Quick revision
- E. coli (75 to 90%), ascending; P fimbriae for adhesion.
- Newborn: boys (uncircumcised); later: girls.
- Infants: fever, vomiting, jaundice, failure to thrive; older: dysuria, frequency, flank pain.
- Culture: 100,000 CFU/mL clean-catch; 50,000 with pyuria by catheter; bags not for culture.
- IV antibiotics for neonates and toxic children; neonates 10 to 14 days; older 7 to 14 days.
- Ultrasound for every febrile infant; MCUG for reflux and valves; DMSA for scars.
- VUR commoner the younger the child; scarring rises with grade; reflux nephropathy causes hypertension and CKD.
- Prophylaxis: trimethoprim or nitrofurantoin at night.
Written by The House Job from standard references (Basis of Paediatrics by Pervez Akbar; Nelson Essentials of Paediatrics).
FAQ
What is the best way to collect urine for culture from an infant?
Urethral catheterisation or suprapubic aspiration; bag specimens are often contaminated and should not be used to make the diagnosis.
Does every child with a UTI need an MCUG?
No. Ultrasound comes first, especially after a febrile UTI in an infant; MCUG is kept for an abnormal ultrasound, recurrent UTI or suspected reflux or valves.
Why does UTI in a young child matter so much?
Infection of a young kidney, especially with reflux, can leave scars that later cause hypertension and chronic kidney disease, so prompt treatment and imaging are important.
When is a DMSA scan useful?
It shows areas of reduced uptake in acute pyelonephritis and, done later, shows permanent renal scars after infection.