Urinary Tract Infection

Urinary tract infections are infections anywhere along the urethra, bladder, ureters and kidneys

Aetiology

Causative organisms

  • E. coli most common - EPEC
  • Proteus mirabilis - produces urease, which breaks down urea to form ammonia
    • Most common cause of UTI in men
    • Increases urinary pH → precipitation of salts → staghorn calculus
  • Psudomonas aeruginosa - associated with catheters and instrumentation, immunosuppressed
    • Most common cause of Catheter-associated UTI
    • Resistant to most oral antibiotics except ciprofloxacin
  • Enterococcus e.g. enterococcus faecalis more common in hospital aquired infection
  • Staphlococcus saphrophyticus - usually affects women of child-bearing age
  • Staph. aureus (uncommon) - usually in bacteraemia

Risk factors

  • Greater incidence in women
    • Short, wide urethra, proximity of urethra to anus, increased risk with sexual activity and pregnancy
  • Catheterised patients
  • Abnormalities of the urinary tract

Classifications

Category
Definition
Uncomplicated UTI
Non-pregnant, immunocompetent women, no structural abnormality
Complicated UTI
Male sex, pregnancy, diabetes, obstruction, catheter, CKD
Recurrent UTI
≥2 in 6 months or ≥3 in 1 year

Pathophysiology

Terminology

  • Acute pyelonephritis is when the infection affects the tissue of the kidney
    • It can lead to scarring in the tissue and consequently a reduction in kidney function
  • Cystitis means inflammation of the bladder, and can be the result of a bladder infection

Bacteria in the normal urinary tract

  • Urine in the kidneys, ureters and bladder is normally sterile
  • The lower end of the urethra is colonised by bacteria (coliforms and enterococci from the large bowel)
  • Bacteriuria is does not always mean infection, especially in elderly patients
    • Important to determine if patient is symptomatic

Routes of infection

  • Ascending route (common) - bacteria from bowel → perineal skin → lower end of urethra → bladder → ureters → kidneys
  • Haematogenous route (uncommon) - bacteraemia/septicaemia seeded into kidneys, multiple small abscesses, bacteria in urine

Natural history

  • Uncomplicated UTI: this is a UTI where the anatomy of the urinary tract is normal, and renal imaging will be normal
    • No underlying condition contributing to infection
    • Unlikely to result in serious kidney damage
  • Complicated UTI:  this will occur in urinary tracts with stones, and also in diabetes
    • The recurrent infections can themselves contribute to stone formation
    • The combination of recurrent infection and urinary tract obstruction can result in sever and rapid kidney damage
    • In these conditions there is a risk of Gram-negative septicaemia

Clinical presentation

  • Dysuria
  • Frequency of urination
  • Nocturia
  • Haematuria
  • Features suggestive of upper urinary tract involvement - fever, loin pain, rigors

Investigations

  • Midstream specimen of urine (MSU)
    • Important as first urine passed is most likely to be contaminated
    • Other urine specimens:
      • 'Clean catch' - children, cognitive, or physical restriction
      • Bag urine - babies
      • Catheter specimen of urine
      • Suprapubic aspiration
  • Dipstick urine may indicate infection in select patients
    • Not suitable for urine of elderly or for urine from a catheter specimen
    • Leukocyte esterase indicates WBC in urine
    • Nitrates indicate bacteria in the urine
    • Protein + blood (not necessarily for infection diagnosis)
  • Lab analysis (more accurate, used in selected cases) - look for polymorphs (pus cells), bacteria +/- red cells
    • Culture of urine - 'significant bacteruria'
    • Mixed growth (2+ organisms) is probably due to contamination

Management

Uncomplicated UTI

  • Cystitis
    • Nitrofurantoin 100mg 2x1 for 5 days
    • Cefadroxil 500mg 2x1 for 3 days
    • Cotrimoxazole 960mg 2x1 3 days
  • Pyelonephritis
    • Ciprofloxacin 500mg 2x1 for 7 days
    • Levofloxacin 750mg 1x1 for 5 days
    • Cotrimoxazole 960mg 2x1 for 14 days
 

Complicated UTI

  • Ceftriaxone 1g/24hr IV
  • Ciprofloxacin 400mg/12hr IV
  • Levofloxacin 500mg/24hr

Special cases

Abacterial cystitis/urethral syndrome
  • Patient has symptoms of UTI
  • Pus in urine, but no significant growth on culture
  • May be early phase of UTI, may be due to urethral trauma, may be due to urethithris due to STI
Asymptomatic bacteriuria
  • Incidental finding
  • Antibiotic treatment is generally not required, especially in the elderly
  • Treatment required in asymptomatic bacteriuria in pregnancy
UTI in catheterised patients
  • Only give antibotics if there is fever/symptoms
  • Unnecessary antibiotics result in the catheter becoming colonised with increasinly resistant organisms

Complications

Acute bacterial prostatitis

  • Rare complication of UTI in men
  • Symptoms of UTI, but may have lower abdominal pain/back/perineal/penile pain and tender prostate on examination
  • Same organisms of UTI
  • Diagnosis - clinical signs + MSSU for C&S (+/- first pass urine for chlamydia/gonorrhoea tests)
  • Management - ciprofloxin for 28 days, trimethoprim 28 days if high C. diff risk