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

Aetiology

Causative organisms

• E. coli most common - EPEC
• Proteus - produces urease, which breaks down urea to form ammonia
  • Increases urinary pH → precipitation of salts → staghorn calculus
• Psudomonas aeruginosa - associated with catheters and instrumentation, immunosuppressed
  • 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

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)