What is Urinary Tract Infection (UTI)


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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.

Urinary Tract Infection (UTI)

Statistics on Urinary Tract Infection (UTI)

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.

Risk Factors for Urinary Tract Infection (UTI)

  • 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 of Urinary Tract Infection (UTI)

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.

How is Urinary Tract Infection (UTI) Diagnosed?

1. Dipstick urinalysis:

This simple test is a simple and accurate means of diagnosis. An elevated level of leucocyte esterase and bacterial nitrites in the dipstick urinalysis is a strong indicator of urinary infection. False positives however do occur.

2. Urine microscopy:

The urine is best obtained by the patient passing a “mid-stream” sample or else extracted by supra-pubic needle aspiration or catheter (if less invasive techniques fail) This specimen is then sent for microscopy, culture and sensitivity in order to reach a definitive diagnosis and accurately guide antibiotic therapy should empirical therapy fail to control the infection.

Prognosis of Urinary Tract Infection (UTI)

Lower urinary tract infections are seldom complicated and complete recovery is expected with a short course of antibiotics. Those patients with an uncomplicated lower urinary tract infection are at no risk of developing renal failure in later life.

Upper urinary tract infections will require admission to hospital for intravenous antibiotics followed by an extended oral course of antibiotics at home following discharge from hospital. Recovery is expected with a variable but commonly small reduction in kidney function.

How is Urinary Tract Infection (UTI) Treated?

The treatment regime for urinary tract infections depends on the location of infection (upper or lower) and the isolated or recurrent nature of the infection.

Single Isolated attack:

  1. Pre-treatment urine sample for culture.
  2. Short term antibiotic therapy – A three to five day course of oral antibiotics should be adequate for any lower urinary tract infection.
  3. Increase fluid intake to at least 2L/day.
  4. Obtain another urine culture at day five to ensure eradication of infection. Antibiotics may be altered at this stage with identification of the bacteria responsible for infection.

Admission to hospital is required if signs of acute pyelonephritis exist such as high fever, loin pain and loin tenderness. These patient will require a course of broad-spectrum intravenous antibiotics followed by a further seven days of oral antibiotics guided by culture and sensitivity. The patient may also require a renal ultrasound, to exclude the presence of an obstructing pyonephrosis.

Recurrent UTI:

Firstly, it must be decided whether the patient is relapsing or becoming re-infected. A relapsed infection implies that the primary treatment was insufficient to eradicate the infection. This is defined as the presence of the SAME bacteria in the urine as was present in the previous infection, within seven days of completing treatment for that infection. Re-infection indicates that the previous infection was cleared, but the patient has developed an entirely new urinary tract infection.

  1. Relapsing infection:Search for a cause (e.g. obstructing stones or scarred kidneys) and treat where possibleBegin intense or prolonged antibiotic therapy for up to 6 weeks. Longer term antibiotics may be required if this fails to control infection.
  2. Re-infection

Review risk factors:

  • Cease the use of diaphragm contraception.
  • Identify and treat atrophic vaginitis in menopausal women.
  • Improve diabetes control.

General measures:

  • Increase fluid intake to 2L/day
  • Pass urine regularly (every 2-3 hours)
  • Pass urine before bedtime and after intercourse
  • Avoid bubblebaths and other bathing chemicals
  • Avoid constipation with high fibre diet and laxatives

If infection persists, other options include:

  • Low dose prophylactic antibiotics for a period of 6-12 months.
  • Self administration of antibiotics should urinary symptoms arise.
  • Intravaginal oestrogen therapy for post-menopausal patients with recurrent UTI.

Urinary Tract Infection (UTI) References

  1. Braunwald, Fauci, Kasper, Hauser, Longo, Jameson. Harrison’s Principles of Internal Medicine. 15th Edition. McGraw-Hill. 2001
  2. Cotran, Kumar, Collins 6th edition. Robbins Pathologic Basis of Disease. WB Saunders Company. 1999.
  3. Kumar P, Clark M. CLINICAL MEDICINE. WB Saunders 2002 Pg 545-549.
  4. Longmore M, Wilkinson I, Torok E. OXFORD HANDBOOK OF CLINICAL MEDICINE. Oxford Universtiy Press. 2001
  5. Pappas PG. Laboratory in the diagnosis and management of urinary tract infection. Med Clin North Am. 1991;75:313.
  6. Pubmed Search Engine – National Library of Medicine.

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