Urinary Tract Infection : Etiology and Pathophysiology

Urinary Tract Infection


Etiology and Pathophysiology

  • Urinary tract above urethra normally sterile
  • Defense mechanisms exist to maintain sterility/prevent UTIs
    • Complete emptying of bladder
    • Ureterovesical junction competence
    • Ureteral peristaltic activity
  • Defense mechanisms
    • Acidic pH (less than 6.0)
    • High urea concentration
    • Abundant glycoproteins
  • Predisposing factors to UTI:
    • Factors increasing urinary stasis
      • Intrinsic obstruction (stone, tumor of urinary tract, urethral stricture, BPH)
      • Extrinsic obstruction (tumor, ibrosis compressing urinary tract)
      • Urinary retention (e.g., neurogenic bladder)
      • Renal impairment
    • Foreign bodies such as:
      • Urinary tract calculi
      • Catheters (indwelling, external condom catheter, ureteral stent, nephrostomy tube, intermittent catheterization)
      • Urinary tract instrumentation (cystoscopy)
    • Anatomic factors
      • Congenital defects leading to obstruction or urinary stasis
      • Fistula (abnormal opening) exposing urinary stream to skin, vagina, or fecal stream
      • Shorter female urethra and colonization from normal vaginal flora
      • Obesity
    • Compromising immune response factors
      • Aging
      • Human immunodeficiency virus infection
      • Diabetes mellitus
    • Functional disorders
      • Constipation
      • Voiding dysfunction with detrusor sphincter dyssynergia
    • Other factors
      • Pregnancy
      • Menopause
      • Multiple sex partners (women)
      • Use of spermicidal agents, contraceptive diaphragm (women), bubble baths, feminine sprays
      • Poor personal hygiene
      • Habitual delay of urination (“nurse’s bladder,” “teacher’s bladder”)
  • Gram-negative bacilli normally found in GI tract: common cause
  • Urologic instrumentation allows bacteria to enter urethra and bladder
  • Organisms introduced via ascending route from urethra that originated from the perineum
  • Contributing factor:
    • Sexual intercourse promotes “milking” of bacteria from perineum and vagina
      • May cause minor urethral trauma
  • Less common routes
    • Bloodstream
    • Lymphatic system
  • Catheter-associated urinary tract infections (CAUTI) are the most common HAI
    • Causes
      • Often: E. coli
      • Less frequently: Pseudomonas species
    • Most are underrecognized and undertreated


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