Urinary Tract Infections

Definition
A Urinary Tract Infection (UTI) is defined as the presence of significant bacteria (usually defined as > 100,000 colony forming units of bacteria (CFU) per ml) and increased white cells (> 10/ul) on microscopic examination of the voided urine. Infection can occur in any part of the urinary system. The most common site involves the lower urinary tract, especially the bladder and is called cystitis.

Epidemiology
Females are more prone to infection than males with a ratio of 1:10. The reason is anatomical as the female urinary tract infection is shorter and much closer to the anal area and gastrointestinal tract. Males over 50 years old frequently get UTI due to prostate enlargement which causes retention of urine. Kidney stones and use of urinary catheters also increase risk of UTI. In Singapore, 50% of females will experience UTI at least once during their life with 20% of women aged 20 -65 years suffering at least 1 attack of UTI per year.

Common pathogens causing UTI
The common gastrointestinal bacteria, Escherichia coli, accounts for almost 90% of community-acquired UTI. Proteus species often cause infection in the kidneys and are associated with stone formation in the urinary tract.

Bacteria may spread in a retrograde manner from the lower urinary tract and involve the upper tract (kidneys). Pregnancy, diabetes and retention of urine caused by obstruction are predisposing factors for upper tract disease. Infective endocarditis and sepsis from distant sites may also involve the urinary tract through bacteremia (bacteria in the blood stream). Chronic UTI may progress from acute infection and cause renal inflammation and scarring which may lead to irreversible kidney damage.

Clinical

  • A strong persistent urge to urinate
  • Smelly urine
  • Frequent urination at night
  • A burning or painful sensation during urination
  • Passing frequent, small amounts of urine and sensation of incomplete emptying
  • Cloudy or reddish-coloured urine
  • Fever and/or chills, flank tenderness and pain and vomiting may indicate kidney involvement

Diagnostic Tests
Diagnosis of UTI is based on the detection of high bacteria counts and increased white cells on microscopic examination of a urine sample. Urine collection should be mid-stream clean catch sample or from urinary catheters. Microscopy of the urine sample will determine if there is UTI by counting number of bacteria and white cells.

Blood tests are necessary if there is fever >38C. These help to determine the severity of infection, evidence of kidney damage and to exclude the presence of bacteria circulating in the blood.

An ultrasound or CT examination of the kidneys may be needed if upper tract involvement is suspected. For recurrent UTIs, a cystoscopy may be performed. This involves insertion of a long thin tube with a lens to visualise the lower urinary tract and bladder.

Treatment
Antibiotics are usually given for 3 days for mild lower tract infections like cystitis. For severe infections, especially involving the kidneys, intravenous antibiotics may be required and the treatment is prolonged. UTIs associated with obstruction by stones in the urinary tract are often serious and many such patients will require hospital admission for intravenous antibiotics and removal of the stone(s).

Prevention
UTIs can be prevented with good hygiene (wiping from front to back and cleansing the genital area after intercourse). Increase fluid intake (>2.5 litres daily) and urinating frequently provides a flushing action that may reduce UTI. Douches have been associated with increased incidence of UTI and should be avoided.
Cranberry juice may have infection-reducing properties through change of urine pH and drinking it daily may help prevent UTI in some patients.

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