Urinary Tract Infections (UTIs)

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What is a urinary tract infection (UTI)?

A urinary tract infection (UTI) is an infection involving the kidneys, ureters, bladder, or urethra. These are the structures that urine passes through before being eliminated from the body.

  • The kidneys are a pair of small organs that lie on either side of the spine at about waist level. They have several important functions in the body, including removing waste and excess water from the blood and eliminating them as urine. These functions make them important in the regulation of blood pressure. Kidneys are also very sensitive to changes in blood sugar levels and blood pressure and electrolyte balance. Both diabetes and hypertension can cause damage to these organs.
  • Two ureters, narrow tubes about 10 inches long, drain urine from each kidney into the bladder.
  • The bladder is a small saclike organ that collects and stores urine. When the urine reaches a certain level in the bladder, people experience the sensation that they have to void, then the muscle lining the bladder can be voluntarily contracted to expel the urine.
  • The urethra is a small tube connecting the bladder with the outside of the body. A muscle called the urinary sphincter, located at the junction of the bladder and the urethra, must relax at the same time the bladder contracts to expel urine.

Any part of this system can become infected. As a rule, the farther up in the urinary tract the infection is located, the more serious it is.

  • The upper urinary tract is composed of the kidneys and ureters. Infection in the upper urinary tract generally affects the kidneys (pyelonephritis), which can cause fever, chills, nausea, vomiting, and other severe symptoms.
  • The lower urinary tract consists of the bladder and the urethra. Infection in the lower urinary tract can affect the urethra (urethritis) or the bladder (cystitis).

In the United States, urinary tract infections account for more than 7 million visits to medical offices and hospitals each year.

  • Urinary tract infections are much more common in adults than in children, but about 1%-2% of children do get urinary tract infections. Urinary tract infections in children are more likely to be serious than those in adults and should not be ignored (especially in younger children).
  • Urinary tract infection is the most common urinary tract problem in children besides bedwetting.
  • Urinary tract infection is second only to respiratory infection as the most common type of infection.
  • These infections are much more common in girls and women than in boys and men younger than 50 years of age. The reason for this is not well understood, but anatomic differences between the genders (a shorter urethra in women) might be partially responsible.
  • About 40% of women and 12% of men have a urinary tract infection at some time in their life.
Medically Reviewed by a Doctor on 6/12/2014

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UTI symptoms

Urinary Tract Infection (UTI) Symptoms

In general, the most common symptoms of a urinary tract infection involve the process of urination:

  • Pain or a burning feeling during urination
  • A feeling of urgency, or feeling the need to urinate frequently

Other, more generalized, symptoms can also accompany a urinary tract infection.


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