Introduction

Bacterial infection of the urinary tract (UTI) is common in the paediatric age group. Its significance is greatest in young children, particularly in the first year or two of life, where the high incidence of upper tract infection (pyelonephritis) and the presence of immature kidneys lead to significant potential for renal scarring (reflux nephropathy). It is unlikely that new scarring occurs after age 5 years.

Data from Sweden suggest that in the first 2 years of life, up to 3% of infants may suffer UTI. Between 1 and 10 years of age 3–8% of girls and < 1% of boys will have at least one urine infection. It is important to remember that recurrences are common. UTI is more frequent in boys than girls in the first months of life, partly because of a higher incidence of obstruction including pelviureteric junction obstruction, thereafter occurring significantly more often in girls (Fig. 16.4.1).

Fig. 16.4.1 Epidemiology of UTI in childhood. Cases recorded in Gothenburg 1960–1966.

Source: Winberg J, Andersen HJ, Bergström T, et al. Acta Paediatrica Scandinavia Supplement 1974;63(Suppl. 252):1?20.

UTI is caused by organisms normally resident in the gut. It is thus an ascending infection that may affect the bladder (cystitis) or upper renal tract (pyelonephritis), which may in turn result in scarring. Neonates are unusual as they may also develop UTI following haematogenous dissemination of organisms.

Renal involvement is associated with:

Long-term complications of renal scarring include: pregnancy-associated problems; hypertension; and, rarely, chronic renal insufficiency (see prognosis section below).

History and examination

In infants and young children with UTI, the clinical history is frequently non-specific and may include irritability, jaundice (neonates), poor feeding or fever without apparent source. Symptoms and signs become more specific with increasing age (Table 16.4.1).

Diagnosis

A reliable urine sample is required to establish the diagnosis of UTI. In older children this is usually accomplished by obtaining a midstream sample. Difficulties arise in children too young to have been toilet trained, who are also the group at highest risk for pyelonephritis and renal scarring.

In infants and toddlers, urine bag samples are unreliable (very high false-positive rate) and should not be used. Clean catch samples are more reliable and are the preferred method for non-invasive urine collection. If samples are required urgently, bladder catheterisation is the most reliable method, though those familiar with the technique can consider suprapubic aspiration (SPA). The yield from SPA is markedly improved by using ultrasound to confirm a full bladder.

Samples should be sent to the laboratory for urinalysis, microscopy and culture. Findings supportive of the diagnosis of UTI include presence of leucocytes and organisms on microscopy and leucocyte esterase and nitrites on dipstick urinalysis. Organisms may be seen on Gram stain. In centres without 24-hour laboratory services, after-hours samples should be sent using a urine dip-slide.

Dipstick urinalysis may be helpful in making a provisional diagnosis of UTI. However, a negative result does not rule out UTI in infancy. One study showed that urinalysis was normal in 50% of infants <8 weeks with confirmed UTI. Another study suggested that dipstick urinalysis was a reliable method of ruling out UTI only after age 2 years.

The traditional definition of pyuria is >5 white blood cells (WBC) per high-power field (centrifuged urine). Another definition is >10 WBC mm^–3 (uncentrifuged urine).

The definition of significant bacteriuria is guided by the method by which the urine specimen was collected (Table 16.4.2), though on occasion genuine UTI may be present with lower colony counts than would usually be considered significant, especially in babies – interpret results in light of history and clinical findings.