Pyelo­nephritis: kidney infection in children

What is pyelonephritis?

Pyelonephritis happens when bacteria travel up the urinary tract, reach the kidney and cause inflammation of the kidney tissue. It is the most serious form of urinary tract infection and almost always comes with fever.

In infants, it is one of the most common bacterial causes of fever without a clear source.

Signs

• fever above 38°C, sometimes with chills,
• in infants: irritability, poor feeding, vomiting, lethargy; sometimes fever is the only sign,
• in older children: flank or back pain, abdominal pain, nausea,
• burning when urinating, frequent urination, foul-smelling urine.

Diagnosis

• Urinalysis and culture from a correctly collected sample (how to collect it),
• blood tests: markers of inflammation and, in severe cases, kidney function,
• ultrasound: the kidneys, dilation of the urinary tract, abscess or obstruction.

Treatment

Antibiotics are started right after diagnosis (once the urine sample has been taken), without waiting for the culture result. A delay of more than 48–72 hours increases the risk of kidney scarring. They are then changed according to the culture result when needed.

• Children who are stable and can take medicine by mouth are usually treated at home with oral antibiotics.
• Babies younger than 2 months and children who are very unwell or vomiting are admitted to the hospital for intravenous antibiotics, then switched to oral medicine once they improve.
• The total duration is usually 4–7 days. A localized kidney infection (focal bacterial nephritis) needs a longer course, about 3 weeks.
• Plenty of fluids, fever reducers.

Fever comes down within 24–48 hours in about 9 out of 10 children. If it doesn’t, the child should be examined again and the ultrasound repeated.

Follow-up tests

In a child who has had pyelonephritis, it is important to find the cause and protect the kidney:

• Ultrasound: for every child after a febrile infection; within 24 hours in infants and very unwell children.
• VCUG (voiding cystourethrogram): to check for reflux, not during the infection. It is considered after a first febrile infection before 12 months of age, with recurrent febrile infections, an abnormal ultrasound or DMSA, or an atypical infection at any age.
• DMSA: to look for kidney scarring, at least 6 months after the infection.
• In toilet-trained children, bladder and bowel habits are checked, because treating dysfunction and constipation lowers the chance of another infection.

Kidney scarring

In some children, the inflamed area of the kidney heals with a scar. If the scar is small, it usually causes no problems. Large or bilateral scars can lead to high blood pressure and reduced kidney function years later. That is why children with kidney scars have their blood pressure and urine checked periodically.