Urinary Tract Infection - UTI


These are very common in women, but far less common in men and children.
Recurrent infection can lead to considerable morbidity and may even lead to renal disease, and possibly end stage renal failure.
It is also a source of life-threatening Gram-negative septicaemia.


  • Urinary tract infections are much more common in women. 50% of women will suffer from a UTI in their lifetime.
  • About 3% of 20 year old women have a UTI at any one time. This increase by 1% with each decade of life.
  • UTI’s are pretty uncommon in men, except during the first year of life, and over the age of 60.
  • UTI’s account for 1-2% of all patients in primary care.
  • About 30% of catheterized patients have a UTI.


  • In women, often the urinary tract is anatomically normal.
  • In contrast, in men and children where UTI’s are much less common, then there often is an anatomical abnormality.
  • Infection is most commonly due to the bacteria in the patient’s own bowel – and the most common route of transmission is up the urethra, although it can get there through blood, lymphatics or a fistula.
  • A UTI infection can affect any part of the urinary tract. The most common place is in the bladder. Site of infection are classified as follows:
    • Bladder – cystitis
    • Prostate – prostatitis – this is the most common site of presentation in the male.
    • Renal pelvis - Pyelonephritis
  • UTI’s are more common in sufferers of diabetes.
  • E. coli is the major cause of UTI’s – it is responsible for >70% of cases in the community, and >41% of cases in hospital.


Symptom severity is determined by the type of bacterial infection, however, tissue damage is due to the level of inflammation and injury caused by the hosts own immune system.
Virulence –this is dependent upon certain characteristics of the infecting organism.to be successful in causing an infection, bacteria should have:

  • Flagellae – for motility
  • Aerobactin – for acquiring iron in an iron poor environment
  • Adhesions – these are the most important as they enable the bacteria to adhere to the epithelial cells of the urinary tract. There are two main types of E. Coli, one with adhesion molecules better suited to the bladder, and the other with adhesion molecules more suited to the renal pelvis.

Other implicated factors

  • Urine pH and osmolality – the greater the osmolality, the less likely the bacteria are to survive. If the pH is particularly high or particularly low then this is also likely to reduce bacterial survival.
  • Commensal organisms – other bacteria are actually involved in normal host defence – they prevent E. Coli from overgrowing. these other bacteria can be killed by spermicidal gel or disruption by antibiotics, and as such, these agents are often advised against.
  • Urine flow / micturition – these wash out bacteria, and thus urine stasis promotes UT infection.

Natural history

  • 90% of UTI’s are isolated events, only 10% are part of a patients recurring infection pathology. Of those with recurring infection, 20% will relapse (this is where the same infection occurs within less than 7 days after treatment), whilst 80% will become re-infected (this is where there is a period of 14 days or more without infection, and then the patient may be infected again, with the same or a different organism – re-infection involves a separate infection, relapse is the same infection that just hasn’t cleared up.)
  • Uncomplicated UTI – this is a UTI where the anatomy of the urinary tract is normal, and renal imaging will be normal. There will be no underlying condition contributing to infection. This is unlikely to result in serious kidney damage.
  • Complicated UTI -  this will occur in urinary tracts with stones, and also in diabetes (as a result of the kidney damage caused by 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.
  • You should always assume in MEN that a UTI is complicated until proven otherwise.

Acute Pyelonephritis

This is acute kidney infection.
This will often present with fever, loin pain, tenderness and significant bacteriuria.
There may be small renal abscesses and streaks of pus in the renal medulla.
Histologically you can see infiltration with leucocytes.
CT scans will often show ‘wedge-shaped’ areas of inflammation, although if treated with antibiotics it will rarely cause permanent kidney damage.

Reflux Nephropathy

This was in the past called chronic pyelonephritis.
It results from a combination of
  • A compromised vesicoureteric valve (the valve that separates the ureters from the bladder)
  • Infection in infancy or early childhood.
Normally, the vesicoureteric junction acts as a one-way valve, allowing urine to enter from above, but not leave the bladder via this route when the bladder contracts.
In some infants and children, this valve is compromised. This results in a jet of urine shooting up the ureter upon emptying the bladder. This is also associated with incomplete bladder emptying, and incomplete bladder emptying predisposes infection. The reflux of urine also leads to kidney damage.
Diagnosis –on CT scan the kidneys will appear irregular, and may be reduced in size. The condition can be unilateral or bilateral, and may affect all or only part of the kidney.
Reflux often subsides around the age of puberty, when the base of the bladder grows, however by this time, the damage may have already been done. Renal function can decline, even if there is no further infection, due to fibrosis of the renal tissue.
If the condition is chronic and does not resolve with age after being acquired in infancy, then it is likely to cause end-stage renal failure in childhood or adult life.
Having this condition in child-hood also predisposes to hypertension in later life.
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