Urinary Tract Infection

See also:

A common, potentially serious, infection in children.  More common in girls over the age of 3 months, more common in boys below that.

Generally occurs by ascending infection from urethra.  Most common organisms are E coli, Klebsiella, Enterococcus faecalis, Proteus.  Infection appears to develop clinically when bacteria in the urine manage to adhere, hence depends on presence of fimbriae on bacterium, and ability of urothelium to resist adhesion (genetic factors).

Classic symptoms are of cystitis:

  • Urinary urgency and frequency (although amounts may be very small)
  • Dysuria
  • Haematuria
  • Suprapubic pain

There may be systemic features, eg fever, nausea/vomiting, lethargy.  However these are more common if the infection progresses to pyelonephritis:

  • unilateral loin pain
  • features of sepsis

Besides the inconvenience, particularly or recurrent cystitis, there is also the risk of long term kidney damage (chronic pyelonephritis, with renal scarring).

Risk factors

  • Constipation
  • Poor fluid intake
  • Withholding of urine for prolonged periods
  • Indwelling catheter

Immunodeficiencies rarely increase risk of UTI, neutrophil disorders are perhaps the exception.


Besides septicaemia, the major complication of concern is renal scarring, with potential for long term chronic pyelonephritis and premature renal failure.

Risk factors are: (n=1280)

  • temperature >=39degC,
  • a bug other than Escherichia coli,
  • abnormal ultrasound
  • neutrophil count >60%, CRP>40 mg/L,
  • Vesico-ureteric Reflux (VUR)

Having 2 or more of the first 3 puts you in a high risk group with double the overall risk of scarring (30 vs 15% in this study).  Covers 21% of the total sample.  Sensitivity is so-so: catches 44.9% of all scarring.

Adding in bloods and/or a micturating cystourethrogram (MCUG) only increases the predictive value by 3-5%. [JAMA Pediatrics. 168(10):893-900, 2014 Oct.  PMID: 25089634]

There are many studies showing that scars can develop without reflux, and that many children with reflux (but without infections) do not develop scars. Scars are associated also with delayed treatment.  Cochrane review did not come out strongly in favour of identifying VUR – nine reimplantations would be required to prevent just one febrile UTI, with no reduction at all in the number of children developing any UTI or renal damage. Archives, 2003

What is the risk of long term damage? Low, given that UTI is common, the occurrence of CRF is rare, and acute pyelonephritis with severe long term complications is also rare. The only large population-based study (n= 1221) found a low risk of hypertension after 16-26 years: only 9% of children with scarred kidneys became hypertensive cf 6% for unscarred. Glomerular filtration rate in later life was normal in both those with and without scarring. Archives of Disease in Childhood 2007;92:357-361

Follow up investigations

Apart from addressing risk factors, you need to consider looking for underlying VUR or else evidence of renal scarring.  See NICE CG54 guidelines.  For Scotland, see SPRUN guidelines.