Urinary tract infection

Last revised by Daniel J Bell on 2 Jul 2019

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. 

  • painful urination
  • strangury
  • bloody, dark, cloudy urine
  • urinary frequency
  • urinary incontinence
  • urinary urgency
  • systemic symptoms: fevers, chills, rigors, tiredness, confusion

UTIs occur when there is bacterial colonization of the uroepithelium and a subsequent inflammatory response. Classically, the urine and urinary collecting system were considered sterile, however, there is some debate on whether a small amount of bacterial colonization is normal 5. 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 mellitus
      • 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 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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