Pyelonephritis in Children (Febrile UTI): Symptoms and When It's an Emergency

A urinary tract infection can occur at two levels: cystitis, which affects only the bladder, and pyelonephritis (kidney infection), which reaches the kidney. In practice, fever is what distinguishes the two in a child: a urinary tract infection with a fever of 38 °C or higher is considered pyelonephritis until proven otherwise.

The most deceptive feature of pyelonephritis is that in a young child it may produce no urinary symptoms at all. Symptoms by age are as follows:

• In newborns and infants: fever with no identifiable cause (sometimes the only symptom), fussiness, poor feeding, vomiting, diarrhea, poor weight gain, prolonged jaundice, foul-smelling urine; rarely, a low body temperature instead of fever
• Ages 1–5: fever, loss of appetite, abdominal pain, vomiting, crying while urinating, frequent urination, new wetting in a child who was previously dry
• In school-age children and adolescents: fever, chills, flank or back pain, nausea and vomiting, burning while urinating, frequent and urgent urination, cloudy or bloody urine
• In a child with a known diagnosis of reflux: every unexplained fever should be checked with a urine culture, even if another source is found

Starting treatment within the first 48 hours when a febrile UTI is suspected has been reported to reduce the risk of scarring; a urine sample should therefore be collected rather than waiting. Seek same-day care, going to the emergency department if necessary, in the following situations:

• Fever of 38 °C or higher in an infant under 3 months (requires urgent evaluation regardless of any apparent source)
• Persistent vomiting, inability to take fluids, or a marked drop in urine output together with fever
• An infant who is excessively sleepy, hard to wake, or, conversely, cannot be consoled
• Chills, pale or mottled-looking skin, rapid breathing
• Severe flank pain, back pain, or abdominal tenderness
• Fever persisting, or overall condition worsening, 48–72 hours after starting treatment
• Fever developing in a child with known kidney reflux, a single kidney, catheter use, or while on antibiotic prophylaxis

The basis of diagnosis is a urinalysis and urine culture taken before antibiotics are started. A culture taken after antibiotics have been given is unreliable, which is why the “sample first, medication second” order is maintained in a feverish child.

Pyelonephritis is treated with antibiotics, and guidelines recommend a total course of 7–14 days; the short courses used for cystitis are not enough for a kidney infection. The medication is changed if needed, based on the culture and sensitivity results.

Every child who has had a febrile UTI undergoes a kidney–bladder ultrasound; this study shows dilation, a duplex system, stones, or bladder problems, but it does not show reflux, and a normal result does not rule reflux out.