Childhood urinary infections

Introduction
Urinary tract infection (UTI) occurs in 2% of boys and 8% of girls by 10 years of age.¹ It causes an acute illness, which may, particularly in babies, be associated with septicaemia. Boys are affected more commonly than girls in the first few months of life.² The incidence in males then falls to a low at two years of age which is maintained until late adult life. The incidence in females persists with peak incidence between 3 and 7 years of age. UTI is associated with renal parenchymal defects (`scarring') which may lead to hypertension or renal failure.³

Bacteriology
Over 80% of UTIs are caused by Escherichia coli. The remainder are due to Proteus, Klebsiella, Enterococcus faecalis and Pseudomonas. Occasionally, other organisms such as Candida or Staphylococcus epidermidis are responsible. The occurrence of Pseudomonas or unusual organisms is usually associated with underlying pathology or prolonged broad-spectrum antibiotic therapy.

Risk factors for the occurrence of urinary tract infection are the presence of urinary stasis (due to neurologic disorder or obstruction), vesicoureteric reflux, bladder dysfunction or chronic constipation.

Presentation
Urinary tract infection may present as unexplained fever at any age, but is most likely to do so in infancy and in the elderly. In infants, other non-specific symptoms and signs may predominate e.g. poor feeding, prolonged vomiting and failure to thrive.² By two years of age, local symptoms predominate e.g. dysuria, frequency and lower abdominal or loin pain. Development or exacerbation of diurnal enuresis may be due to UTI, although nocturnal enuresis is only rarely associated with infection. Loin pain associated with fever strongly suggests the presence of renal parenchymal infection, although the kidney may be affected in the absence of localising symptoms.

Perineal, vulval or penoscrotal inflammation and irritation are not usually due to UTI, but to threadworm infestation or other local irritants including forceful retraction of a healthy foreskin in boys and frequent use of harsh soaps in girls. This irritation is another cause of dysuria.

Diagnosis
The diagnosis requires the identification of significant numbers of viable bacteria in a reliable urine specimen. Dipstick testing of the urine for nitrite and leucocyte esterase will suggest the diagnosis in a high proportion, but it is not known which cases will be missed.⁴ A formal urine culture is required and, if dipstick screening is used, this will often mean obtaining another specimen.

Reliable specimens are the midstream specimen or a specimen collected by catheterisation or percutaneous needle aspiration of urine from the bladder. Obtaining midstream specimens from children under two years of age is difficult, but can be achieved if someone, usually a parent, has time to sit with the child and catch a urine specimen in a sterile container when the child voids spontaneously.

Catheterisation for collection of a urine specimen may be done with a 5 FG soft feeding tube. The catheter should be introduced only far enough to allow urine to be collected. If several centimetres of a fine catheter are introduced, it may knot in the bladder and require surgical removal. Needle aspiration from the bladder should not be attempted if the child has passed urine within the past hour or if there is a suspicion of oliguria.

Specimens collected into applied plastic bags (`bag specimens') are unsatisfactory for diagnosing urinary infection.

The specimen must be cultured without delay or be refrigerated if there is to be a delay.

The culture of a midstream urine specimen is positive when there is a single organism present and the colony count is >108organisms/L of urine. The presence of any organisms in catheter and needle aspiration specimens usually indicates the presence of infection. The presence of multiple organisms suggests contamination either due to collection technique or the presence of a fistula between the urinary and intestinal tracts.

Screening and asymptomatic bacteriuria
Approximately 2% of schoolgirls may have bacterial colonisation of the urinary tract in the absence of symptoms. This is asymptomatic bacteriuria. Treatment with antibiotics has not been effective in preventing renal scars and may increase the risk of symptomatic UTI.⁵ Screening of children is therefore not recommended.

Treatment (Fig. 1)

Antibiotics (Table 1)
Antibiotic therapy is based on the known sensitivity patterns of the usual causal organisms. At present, over 85% of the commonly isolated organisms are sensitive to gentamicin, sulfamethoxazole/trimethoprim, cephalexin, cefotaxime, amoxycillin/clavulanate, and nitrofurantoin. Trimethoprim syrup is recommended in some countries, but is not available in Australia. Nitrofurantoin suspension is associated with gastrointestinal adverse effects in a significant number of children and should not be given to patients with reduced renal function.

Antibiotic therapy may begin before culture results are available. Most children can be treated with oral antibiotics for 5 days. Children with UTI who are systemically unwell, who have a history of anatomical abnormalities of the urinary tract or who have had recent urinary tract instrumentation should be admitted to hospital. They are treated with intravenous antibiotics until afebrile for 24 hours and taking oral fluids normally. They may then change to oral antibiotics which should be continued for another 5 days.

Children with their first confirmed UTI should continue on a prophylactic dose of antibiotic until investigations are complete. Following completion of full dose treatment, a urine culture should be done to ensure that the infection has been eradicated without suspending any prophylaxis.

Investigation (Table 2)
Anatomical abnormalities are associated with renal parenchymal abnormalities in children with urinary tract infections.6 Children are investigated for the presence of such abnormalities in the hope that surgical correction of these defects or prevention of further urine infections will prevent renal damage. Correction of significant obstruction is clearly important, but interventions for children with vesicoureteric reflux have never been subjected to placebo-controlled trials.

At present, it is recommended that all children with a first UTI be investigated. A plain x-ray of the abdomen and a renal ultrasonograph should be done to exclude urinary tract obstruction, calculi and significant skeletal abnormalities e.g. lumbosacral abnormalities. As it appears that the risk of renal parenchymal defects in association with vesicoureteric reflux occurs mainly in early childhood,⁶ most protocols only include a micturating cystourethrogram for children under 4-5 years of age. A recent systematic review of all studies concluded that there was a need for studies to determine if such investigation is beneficial.⁷ Other investigations may be indicated by the clinical presentation.

As 15% of children with renal cortical defects at the time of their first UTI do not have reflux, it has been suggested that isotope scanning with dimercaptosuccinic acid (DMSA) may be a more logical investigation (see box).

Radio-labelled DMSA is taken up and retained in the kidney for some hours after it has been cleared from the circulation and other tissues. As a result, DMSA scans are very sensitive to the presence of cortical defects. The precise significance of small defects is uncertain. Some defects seen at acute presentation of urine infection are persistent and some disappear. It is unclear at this time what proportion of persistent defects are the result of acute infection and how many are congenital.

Prevention
As recurrent childhood infections may damage the kidneys, prevention is indicated.

Antibiotic prophylaxis (Table 1)
Long-term urinary prophylaxis with sulfamethoxazole/trimethoprim, cephalexin or nitrofurantoin has a high degree of safety, but may not be effective. There is a need for randomised, double-blind, placebo-controlled trials of antibiotic prophylaxis in children with urinary tract infection with and without vesicoureteric reflux.

Circumcision
Urine infection is more common in uncircumcised boys. On the basis of observed risks, it has been calculated that to prevent one urine infection, 99 boys must be circumcised and up to 5 will have some complication of the circumcision.⁸ Prevention of UTI is not an indication for routine circumcision, but may be recommended for boys with recurrent infections or major renal abnormalities complicated by UTI.

Other approaches
Therapy to minimise bladder instability, particularly in preschool and primary school girls with recurrent bladder infections, may be useful. This may include relief of constipation, modification of the environment or anticholinergic drug therapy.

For neuropathic bladders, intermittent catheterisation and occasionally surgery are required in addition to prophylactic antibiotics.

Follow-up
Children with vesicoureteric reflux usually continue prophylaxis until they are 4 or 5 years old. Some paediatric nephrologists recommend a follow-up micturating cystourethrogram; others rely on follow-up DMSA scan to determine long-term follow-up. Children with permanent renal scars are at risk of early onset hypertensionand should be monitored with annual urinalysis and measurement of blood pressure.

Children with urinary obstruction or calculi should be referred for a urological opinion, as should those with vesicoureteric reflux and recurrent infections in spite of prophylactic antibiotics.