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Urinary Tract Infection

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Also known as: UTI

What is a urinary tract infection?

A urinary tract infection (UTI) is an infection of one or more components of the urinary tract. The urinary tract consists of two kidneys, two ureters, a bladder, and a urethra. Thumbnail diagram of normal urinary tractThe kidneys are bean-shaped organs found in the lower back below the ribcage. They filter waste out of the blood and produce urine to carry the wastes and excess water out of the body. The urine is carried from the kidneys, through the ureters, and into the bladder. The bladder is a hollow muscular organ that stores urine for a short period. The bladder stretches as urine accumulates and, at a certain point, it signals the body to relieve the growing pressure. A muscular sphincter valve at the opening of the bladder is relaxed and the bladder contracts to send urine through the urethra and out of the body.

The blanket term UTI is frequently used, but a urinary tract infection may also be identified by the part of the urinary tract affected. Urethritis is an inflammation and/or infection of the urethra. Bladder involvement is called cystitis, and when one or more of the kidneys are inflamed or infected, it is called pyelonephritis.

Urine does not normally contain microorganisms, but if it is obstructed leaving the body or retained in the bladder, it provides a good environment for bacteria to grow. Most urinary tract infections are due to bacteria that are introduced into the opening of the urethra. They stick to the walls of the urethra, multiplying and moving up the urethra to the bladder. Most UTIs remain in the lower urinary tract (urethra or bladder), where they cause symptoms such as urinary urgency and a burning sensation during urination. Most of these infections are considered uncomplicated and are easily treated, but if they are not addressed, the infection may spread up through the ureters and into the kidneys. A kidney infection is more dangerous and can lead to permanent kidney damage. In some cases, a urinary tract infection may lead to an infection in the bloodstream (sepsis, septicemia) that can be life-threatening. Rarely, a bloodstream infection may infect the kidneys.

Although a variety of bacteria can cause UTIs, most are due to Escherichia coli, a bacterium that is common in the gastrointestinal tract and is routinely found in stool. Other bacteria that may cause UTIs include species of Proteus, Klebsiella, Enterococcus, and Staphylococcus. Occasionally, a UTI may be due to a yeast, such as Candida albicans; urethritis is often due to a sexually transmitted disease such as herpes, chlamydia, or gonorrhea.

Urinary tract infections are common. According to the American Urological Association Foundation, UTIs result in more than 7 million visits to doctor's offices a year. Although they can affect anyone at any age, women are much more likely than men to have a UTI with about 40% of women and 12% of men having at least one in their lifetime. It is thought that a woman's increased susceptibility is partly anatomical, because the woman's urethra is shorter and because their anus and vagina are relatively close to the urethra. Anything that slows down the passage of the urine, blocks it, or introduces bacteria into the urinary tract can raise a person's risk of having a UTI. Conditions that cause an increased risk for developing a UTI include:

  • Anatomical problems, such as narrowing of the urethra or ureters
  • Urine retention (the bladder does not empty completely)
  • Vesicoureteral reflux (the abnormal flow of urine from the bladder back to the ureters)
  • Kidney stones
  • Bladder catheterization, especially long term
  • Spinal cord injuries
  • Diabetes - it causes changes to the immune system, damage to the kidneys, and often results in sugar in the urine, promoting the growth of bacteria
  • Kidney disease
  • Kidney transplant
  • Any condition that suppresses the immune system
  • In men, an enlarged prostate may inhibit the flow of urine.

In most cases, UTIs are acute and uncomplicated. They are treated and the symptoms subside within a day or two. UTIs that spread to the kidneys, however, may cause permanent kidney damage, especially in the elderly and the very young. Conditions or diseases that result in chronic or recurrent UTIs may damage the kidneys and, in some cases, cause kidney failure. Renal failure and septicemia can be life-threatening conditions. They require immediate treatment, which often involves hospitalization. In pregnant women, a UTI can lead to premature labor and delivery and cause high blood pressure. In men, a UTI can cause prostate infection and inflammation, which can be difficult to treat.

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