Virtual Medical Centre

Urinary Tract Infection (UTI)

• What is Urinary Tract Infection?
• Who gets Urinary Tract Infection?
• Predisposing Factors
• Progression
• Probable Outcomes
• How is Urinary Tract Infection Diagnosed?
• How is Urinary Tract Infection treated?
• Urinary Tract Infection References
• Drugs/Products Associated with Urinary Tract Infection

What is Urinary Tract Infection?

A urinary tract infection (UTI) occurs in the urinary tract, this includes those parts of the urinary system between the kidneys and the external environment. These include the ureters, (connecting each kidney to the bladder) the urinary bladder, and the urethra (allowing the passage of urine from the bladder to the external environment.)

A urinary tract infection can occur at any one of these anatomical sites. An "upper" urinary tract infection is defined as any infection above the bladder (i.e. within the ureter and/or renal collecting system.) The "lower" urinary tract infection is defined as infection of the urinary system at the level of, or below the bladder.

Who gets Urinary Tract Infection?

Urinary tract infections commonly occur in women but occur infrequently in the male population. The increased rate of urinary infection in the female population is explained by the difference in length ofthe male and female urethra. Most urinary tract infections occur when bacteria ascend from the genital region through the urethra and into the urinary bladder above.

The average female urethra is approximately 4cm long, permitting easy entry of bacteria into the bladder and cause infection. The average male urethra is 15-20cm long, providing better protection against infection by way of its increased length. Besides the increased physical distance bacteria must travel to cause infection, the male urethra has a greater surface area to secrete antibodies to combat infection of the urinary tract.

Urinary tract infection also has special significance in children for a number of reasons. Firstly, urinary tract infection is less easily diagnosed and thus more likely to progress to a serious extent if the problem infection is not treated. Also, urinary tract infections during childhood may be the first sign of "vesico-ureteric reflux" in which urine is allowed to flow back from the bladder to the kidneys. If left untreated, these patients may develop long-term kidney problems. When managed appropriately however, these long term problems are most often avoided.

Predisposing Factors

• Diabetes Mellitus
• Pregnancy
• Impaired passage of urine: e.g. secondary to prostate enlargement, stricture of the urethra, kidney stones
• Urinary catheters
• Frequent sexual intercourse
• Diaphragm use
• Menopause

Progression

The urinary tract infection is usually an isolated event, which will never recur in 90% of patients affected. In the vast majority of cases, the simple lower urinary tract infection will be easily treated with a 3-5 day course of oral antibiotics. Upper urinary tract infections may require admission to hospital for a short course of intravenous antibiotics with an oral course to be completed on discharge. The symptoms of infection will gradually subside of the course of treatment.

Recurrent urinary tract infections therefore occur in 10% of patients following their first event. The significance of recurrent infection is determined through assessment of urinary tract function. If the urinary tracts are normal, there is little chance that infection will spread to the kidneys and cause renal impairment. If the urinary tracts are abnormal (e.g. renal stones) and an associated disease such as diabetes is present, the infection will more likely spread to the kidneys where repeat infection will result in long-term renal impairment.

Acute Pyelonephritis:

If infection ascends from the bladder to the kidneys, acute pyelonephritis may result. In this condition, bacteria begin colonising the tubules and connective tissue of the kidney itself. Small abscesses and streaks of pus begin to appear in the renal cortex and medulla respectively. With the appropriate use of antibiotics, it remains unusual for pyelonephritis to cause any long-term renal damage is adults with normal urinary tracts.

The complications of acute pyelonephritis occur in special circumstances.

1. Papillary necrosis: Occurs mainly in diabetics and patients with urinary tract obstruction. This condition is usually bilateral causing necrosis of one or all of the pyramids of the affected kidney. On cut section, the tips or distal 2/3 of the pyramids appear grey-white to yellow indicating that tissue infarction has occurred.
2. Pyonephrosis: Seen with total urinary tract obstruction where the suppurative exudate of the infection is unable to escape from the urinary tract, accumulating proximal to the urinary obstruction.
3. Perinephric abscess: Occurs when infection spreads through the renal capsule and into the perinephric tissues.

After the acute phase of infection, healing inevitably occurs. The inflammatory foci are replaced by scars that may be seen on macroscopic examination as indentations on the cortical surface of the affected kidney. The underlying kidney structure is distorted in the presence of this scar, reducing renal function in this area, and contributing to an overall reduction of global renal function.

Chronic Pyelonephritis (AKA Reflux nephropathy or Atrophic pyelonephritis):

This condition occurs only in those patients with have suffered vesico-ureteric reflux (see "Incidence" above) and urinary tract infection in infancy and early childhood. The condition occurs when the vesico-ureteric reflux passes unnoticed and a child endures numerous urinary tract infections throughout their childhood. Typically, reflux will cease during puberty along with urinary tract infections, with pubertal growth of the bladder base. The damage of recurrent kidney infections will persist and progress, as fibrosis occurs and progressive loss of renal function occurs.