11: Urinary Tract Infections

Question 1

Define a urinary tract infection.

Answer 1

• Significant bacteriuria in presence of constellation of symptoms:
  
  • Dysuria (painful urination)
  • Increased urinary frequency/urgency
  • Suprapubic discomfort
  • Costovertebral angle tenderness
• Lower UTI (acute cystitis, urethritis, prostatitis): infx of bladder/urethra; sx = dysuria, suprapubic tenderness, urinary frequency/urgency, low back pain, bladder fullness/discomfort, hemorrhagic cystitis (10%)
  
  • If sexually active woman, must rule out gonorrheal/chlamydial urethritis, especially if sx of vaginal discharge
• Upper UTI (acute pyelonephritis, intra-renal abscess, perinephric absecc): infx in kidney and renal pelvis; sx = flank pain, fever, sweating, dehydration, hypotension, dysuria, urinary urgency/frequency

Question 2

Distinguish complicated vs. uncomplicated UTI.

Answer 2

• Uncomplicated: absence of known predisposing conditions; infection in structurally and neurologically normal urinary tract; simple cystitis of 1-5 day duration.
• Complicated: occur in patients w/ underlying, predisposing condition (medical, functional, anatomic) that increases risk of initial infection and recurrence; reduces therapy efficacy; more abx-resistance

Question 3

Give the epidemiology of UTI’s.

Answer 3

• Increased risk:
  
  • Neonates (males)
  • Prepubertal girls
  • Young women
  • Older men
  • Structural abnormalities of UT
  • Immunosuppresion (diabetes)
• In sexually active women, mostly caused by E. Coli or Staph saprophyticus.
• In catheterized patients, GP organisms (Enterococcus spp) and coag-neg staph more common.

Question 4

Describe the pathogenesis of UTIs.

Answer 4

• Hematogenous Route: Infx of renal parenchyma by blood-borne organisms; kidney abscess in pt w/ bacteremia or endocarditis caused by GP S. aureus.
• Ascending Route
  
  • Colonization of periurethral area with uropathogenic bacteria (fecal flora)
  • Urethral colonization
  • Bladder inoculation
  • Cystitis, urethritis
  • Pyelonephritis

Question 5

Describe the bacterial virulence factors.

Answer 5

• Enhanced adherence to receptors on uroepithelial cells: Type 1 fimbriae, P fimbriae
• Phase variation: Type 1 fimbriae = facilitate attachment to bladder epithelium but phagocytosed, P fimbriae = block phagocytosis, expressed in renal parenchyma; in upper UTIs, Type 1 downreg’d, Type P upreg’d.
• Flagella: enhanced motility
• Hemolysin: pore formation in cells –> cell lysis –> nutrient release
• Aerobactin (siderophore): iron acquisition in otherwise iron-poor environment of UT

Question 6

Describe the diagnosis of UTIs.

Answer 6

• Urinalysis: presence of WBCs (pyuria), RBCs (hematuria), bacteria (bacteriuria)
  
  • In sexually active young women, presence of pyuria, hematuria or bacteriuria highly suggestive of UTI; diagnose cystitis w/o urine culture
  • >10 leukocytes/microliter urine indicates infection
• Urine dipstick test: leukocyte esterase + (pyuria), nitrite + in 25% (bacteria)
• Urine leukocyte esterase test: rapid screen for pyuria, nitrite
• Microbiological analysis = gold standard
  
  • Bacteria > 10⁵/mL urine indicates infection
• Proteinuria suggests complicated cystitis or upper UTI
• Low margin of error in Rx for children, pregnant women
• Radiographic studies (ultrasound, IV pyelography, CT) for pts with abnormalities of UT, suspected abscess, pt with pyelonephritis that does not respond within 72 hours

Question 7

Describe the treatment of UTIs.

Answer 7

• Lower UTI in health female with sx of recent onset: oral abx for 3 days; all other women, 5-7 days
• For acute pyelonephritis: IV w/ completion PO after afebrile (total duration 10-14 days); repeat urine culture 5-9 days post-therapy (if positive, Rx 2-4 weeks)
• TMP-SMZ (Bactrim) & fluoroquinolones (cipro/levofloxacin) ideal agents

Question 8

Describe candiduria.

Answer 8

• Presence of candida (fungus) in urine.
• Seen primarily in catheterized pts, often asymptomatic.
• Rx for infx that do not resolve post-catheter: oral fluconazole, bladder irrigation w/ ampB