Urinary tract infection

Dr Henry Knipe and Dr Matt A. Morgan et al.

Urinary tract infection (UTI) is a common clinical condition involving the bladder (cystitis) and kidneys (pyelonephritis). It is commonly divided into 'uncomplicated' and 'complicated' infections. 

UTIs occur when there is bacterial colonisation of the uroepithelium and a subsequent inflammatory response. Classically, the urine and urinary collecting system is sterile, although there is some debate whether a small amount of bacterial colonisation is normal. Given this, and that voiding urinary samples may be contaminated by skin or rectal reservoir flora, bacteriuria is suggestive of a UTI, but bacteriuria and pyuria (white blood cells in the urine) is much more specific for infection.

  • uncomplicated: an otherwise healthy patient with a structurally and functionally normal urinary tract
  • complicated: factors are present that decrease the likelihood of therapy being effective
    • urinary tract is structurally or functionally abnormal
    • immunocompromised status
    • especially virulent pathogen
    • factors that may make a patient complicated 1
      • male
      • childhood UTIs
      • immunocompromised
      • pregnancy
      • elderly
      • diabetes
      • failed antibiotic course
      • extended symptoms before presentation

These patients are usually well managed with a course of oral antibiotics.

Many imaging algorithms suggest that imaging for an uncomplicated cystitis or pyelonephritis is unnecessary.

These patients have often failed a course of antibiotics and may benefit from imaging:

  • lower urinary tract
    • CT urography: for evaluation of structural abnormalities and possible abscess formation; MRI could be considered if the patient has an allergy to contrast
    • ultrasound has a secondary role
  • upper urinary tract
    • CT abdomen with contrast (or without and with contrast)
    • MRI abdomen: for patients with contrast allergies and pregnant patients
    • renal and bladder ultrasound: second line, relative to CT it is not as good at detecting renal parenchymal changes and/or characterizing perinephric extension of infection
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Article information

rID: 40521
System: Urogenital
Section: Approach
Synonyms or Alternate Spellings:
  • Urinary tract infections
  • UTIs
  • UTIs

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