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Understanding Urinary Tract Infections -- the Basics

What Are Urinary Tract Infections?

Urinary tract infections (UTIs) are bacterial infections in the body's urinary system -- the bladder, kidneys, ureters, and urethra. In the kidneys, the infection is called pyelonephritis; in the bladder, it is called cystitis. 

The basics on urinary tract infections from WebMD.

Urinary tract infections are common in women. Children with UTIs may show different symptoms than adults.

Am I at Risk for a Urinary Tract Infection?

People with a higher risk of developing urinary tract infections include:

  • People with conditions that affect the bladder's nerve supply (including diabetes, multiple sclerosis, Parkinson's disease, and spinal cord injuries)
  • Older adults
  • Pregnant women
  • People who have any kind of obstruction blocking the passage of urine, such as a tumor, kidney stone, or an enlarged prostate
  • Those who use a contraceptive diaphragm or spermicide for birth control
  • People who use a catheter, a tube placed into the bladder to drain urine from the bladder into a bag outside of the body
  • Men who engage in anal intercourse, who have HIV infection, or who have never been circumcised

Most of the risk factors listed also increase the chance that a simple bladder infection may quickly become to a more serious kidney infection, or to sepsis (an infection that has entered the bloodstream). Pregnant women with kidney infections have a greater chance of delivering their babies prematurely.

What Causes Urinary Tract Infections?

Bacteria that are normally found in the gastrointestinal tract, such as E. coli, cause most urinary tract infections. Other bacteria that can cause urinary tract infections include staphylococcus, proteus, klebsiella, enterococcus, and pseudomonas.

Some bladder infections in both men and women have been linked to two sexually transmitted organisms: Chlamydia trachomatis and mycoplasma. Another sexually transmitted organism, trichomonas, can cause similar symptoms.

Women are more likely to get urinary tract infections, because the tube running from the bladder to the outside (the urethra) is much shorter than in men. Because the urethral opening is relatively close to the anus in women, bacteria from stool can easily contaminate the female urethra. A urinary tract infection in young women may be associated with sexual activity.

In men, however, a bladder infection is almost always a symptom of an underlying disorder. Often, the infection has migrated from the prostate or some other part of the body, signaling problems in those locations. Or it may mean that a tumor or other obstruction is interfering with the urinary tract.

Chronic kidney infections in children are sometimes caused by a structural problem that allows urine to flow back from the bladder to kidneys (reflux), or by an inability of the bladder to empty completely.

WebMD Medical Reference

Reviewed by Trina Pagano, MD on March 25, 2014

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