Diagnosis & Pathogenesis

Diagnosis of UTI in Women

  • The most helpful laboratory guide for rapid diagnosis is careful microscopic examination of the urine.
  • Documentation by urine culture can be helpful in diagnosing a first infection or evaluating patients with recurrent symptoms unresponsive to empirical therapy
  • If hematuria is noted, the physician is obligated to be sure that it is no longer present after treatment of infection. If it is still present, a urologic imaging study and cystoscopy are necessary to rule out other urologic pathology
  • If a complicated UTI is suspected by history, a similar evaluation may be necessary after the infection has cleared.



Pathogensis of UTI in Women

  • The bacteria responsible for urinary tract infections are normally present in the bowel
    • Escherichia coli is the most common, accounting for 85 percent of community-acquired infections and up to 50 percent of nosocomial infections
    • Proteus sp., Klebsiella sp., Enterococcus faecalis, and Staphylococcus saprophyticus
    • The female urethra is short, and bacteria generally enter the bladder in an ascending fashion
  • Host defense mechanisms
    • More important than bacterial virulence or inoculum size in determining whether a clinical infection develops.
    • Estrogens and pH affect attachment and colonization of the vaginal mucosa
    • Antiadherence properties of the vaginal and bladder mucosa
    • Hydrokinetic clearance of bacteria through voiding
    • Changes in urine pH and composition that may inhibit bacterial growth
  • Newly recognized intracellular bacterial biofilm-like pods on the bladder surface, resistant to normal host-defense mechanisms, may account for bacterial persistence in some patients prone to recurrent infection.
  • Women with recurrent urinary tract infections demonstrate increased adherence of bacteria in vitro to uroepithelial cells when compared to findings in women who have never had an infection. Studies suggest that this may be genetically determined.
  • Risk factors
    • Sexual intercourse
    • Use of a diaphragm or cervical cap
    • Spermacidal jelly
    • ABO-blood group nonsecretor phenotype
    • Urologic instrumentation
    • Diabetes
    • Age-related changes in the elderly patient
      • Low estrogen levels allow vaginal pH to rise, resulting in a higher likelihood of vaginal colonization with E. coli



Pathogenesis of UTI in Men

  • Common pathogens
    • Gram-negative enteric bacteria cause 80% of UTI in males
      • Escherichia coli most common pathogen
      • Klebsiella, Enterobacter, and Proteus
    • Twenty per cent caused by gram positive organisms
      • Enterococci and staphylococci most common
    • Polymicrobial infection may be associated with:
      • True bacterial prostatitis
      • Diabetes mellitus
      • Urinary fistula between gastrointestinal tract and genitourinary tract
      • Infected foreign body, calculi
  • Most infections in males ascend through the urethra rather than have a hematogenous or lymphatic origin
  • Natural host resistance mechanisms
    • Bladder washout of bacteria during micturition (ineffective in presence of urinary residual)
    • Bacterial antiadherence factors.
      • Luminal mucopolysacharide layer of bladder inhibits bacterial adherence
    • Normal urethral flora
      • Tamm-Horsfall mucoprotein
      • Immunoglobulins IgA and IgG
    • Long relative length of male urethra as compared to female, and its protected position in relation to perineum helps prevent bacterial ascent.
    • Prostatic antibacterial factor. Secreted by the prostate. Spermine has some activity against gram-positive bacteria. Zinc may be antibacterial.



Localization of UTI in Men

  • The four-glass urine test differentiates urethritis, bacterial cystitis and chronic bacterial prostatitis
  • The uncircumcised male must retract his foreskin prior to voiding and wipe glans with an alcohol swab. The first 10 mL of urine is collected in a sterile specimen container [voided bladder l (VB 1)]. After voiding 200 mL, a midstream specimen is collected in a separate container (VB2). The patient then stops voiding and prostatic massage is performed. The expressed prostatic secretion (EPS) is gently milked by proximal to distal pressure on the bulbar urethra and is collected in a fresh container. The next 10 mL of voided urine is collected immediately following prostatic massage (VB3).
    • VB1 identifies the urethral flora and shows the highest amount of growth in the presence of bacterial urethritis or asymptomatic colonization.
    • A positive VB2 culture can indicate either a bacterial cystitis, bacterial prostatitis, or urethritis. Treatment with an antibiotic that has poor penetration into the prostate (nitrofurantoin) should sterilize the bladder urine VB2, and permit better localization of the infection with a repeat localization study.
    • EPS and VB3 colony counts tenfold higher than VB1 indicate prostatic infection when VB2 culture is negative.
  • It is probably unnecessary to perform this test in a patient with a negative urine culture and no history of previous culture documented urinary tract infection, as the incidence of chronic bacterial seeding of the urinary tract emanating from the prostate is extremely low in this circumstance.



Diagnosis of Bacterial Cystitis

  • Urinalysis showing positive leukocyte esterase and nitrite on dipstick and greater than 10 white blood cells per high power field on centrifuged urine specimen strongly suggests infection.
  • Urine culture showing greater than 104 colony forming units of a pure culture per mL is evidence of true bacterial infection of the bladder as opposed to contamination from the urethra flora.
  • Upper tract imaging with a renal ultrasound (or intravenous urogram if hematuria is present) can rule out infection stones or anatomic abnormality that might predispose to infection.
  • Bladder ultrasound can determine if incomplete emptying (post void residual) is a possible predisposing factor for UTI.
  • Once the urine has been sterilized, cystoscopy can be considered, especially in the setting of hematuria or recurrent UTI.



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