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Causes of recurrent urinary tract infection (UTI)

What is a recurrent Urinary Tract Infection (UTI)?

Recurrent urinary tract infection has been defined as:

  • 3 or more episodes of UTI within the last 12 month period or
  • 2 or more episodes of UTI within the last 6 months

Some studies estimate that 20 to 30% of women who have a UTI will end up having recurrent UTIs.

Is it really a UTI?

It is important to confirm a UTI with a urine specimen (MSU- mid stream urine specimen).

“Cystitis” or bladder inflammation is most commonly caused by a UTI, but there are many other conditions that can cause similar symptoms. Some patients are treated for recurrent UTIs when the actual problem is not urinary infection at all but one of the following problems:

Which Bacteria cause UTI?

Escherichia coli (E.coli) is the most common cause of UTI and is responsible for about 80 to 85% of all UTIs. Other bacteria involved in UTIs include Staphylococcus saprophyticus, Klebsiella, Pseudomonas and Enterococcus. UTIs are rarely due to viral, fungal and parasitic infections.

It is thought that in women who experience recurrent bacterial UTI that the normal healthy bacteria that live in the vagina are replaced by “uropathogenic” bacteria from the bowel. Uropathogenic bacteria have features that make it easier for them to enter, breed and survive in the urinary tract.

Why are Women more commonly affected by UTIs?

Women are more commonly affected by UTIs because of:

  • The female anatomy
    • The female urethra (urine pipe draining urine from the bladder) is short which allows easier entry of skin and surface bacteria into the bladder.
    • The female urethra is close to the vagina and back passage that normally contain bacteria and makes it easier for bacteria to enter the urinary system.
  • Sexual intercourse can make it easier for bacteria to stick to the urethra and then later enter into the bladder.
  • After menopause the drop in oestrogen levels causes changes in the tissues of the vagina and urethra that make them drier and make it easier for urinary tract bacteria to colonise or live in the area.

Predisposing factors for recurrent UTI

Risk factors for recurrent UTIs in younger women include:

  • Sexual intercourse
    • Which makes it easier for bacteria to enter the urinary tract
  • Use of spermicides and diaphragms as contraception
    • Due to the change in the balance of the normal healthy bacteria in the vagina
  • Past history of childhood UTIs
  • Structural abnormalities in the urinary tract such as:
    • Urethral diverticulum (abnormal area or outpouching in the female urethra)

Risk factors for recurrent UTIs in postmenopausal women include:

  • Post menopausal changes in the vaginal tissues (known as “atrophic vaginitis”) which make:
    • Vaginal and urethral tissues thinner and more fragile
    • Results in a change in the balance of the normal healthy bacteria in the vagina
  • Large bladder prolapse that can result in poor bladder emptying. Normal bladder emptying is one of the protective mechanisms that helps flush out bacteria from the bladder.
  • Age related changes in bladder function which can result in poor bladder emptying
  • Urinary incontinence
  • A history of UTIs before the menopause.

Risk factors for recurrent UTIs in men include:

  • Blockage in the urinary tract e.g.:
    • Due to benign enlargement of the prostate gland
  • Poor bladder emptying

Risk factors for UTIs in women and men of all ages include:

  • Blockage or structural abnormalities anywhere in the urinary system
    • Some of these may be congenital (i.e. present since birth)
    • Some of these may be acquired e.g.:
      • Past surgery to treat stress incontinence in women which has caused blockage of urine draining from the bladder
      • Enlargement of the prostate with ageing that occurs in men
  • Stones in the urinary tract
  • Vesicoureteric reflux
    • A faulty valve in the ureter (the drainage tube between the kidney and bladder) which allows urine to pass back to the kidney from the bladder)
  • Catheters - a drainage tube from the bladder
  • Conditions which suppress normal immune system function e.g.:
    • Diabetes
    • Kidney failure

In many women, no structural abnormalities of the urinary tract are evident. In these women it is likely that they have genetic factors predisposing them to recurrent UTIs related to their local immunity against the bacteria that commonly cause UTIs. For example the receptors on their surface cells in the urinary tract may be “stickier” for bacteria than average, which is the first step in bacteria gaining entry to the bladder.

Women with recurrent UTIs have an increased frequency of UTI in close female relatives (such as mother and sisters), which supports a genetic predisposition.