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