Dr. Stacy McBroom
Dr. John Upshaw
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Urinary Tract Infection

Overview

Urinary tract infection (UTI) is a common infection that usually occurs when bacteria enter the opening of the urethra and multiply in the urinary tract. The urinary tract includes the kidneys, ureters (tubes that carry urine from the kidneys to the bladder), bladder, and urethra (tube that carries urine from the bladder). The special connection of the ureters at the bladder help prevent urine from backing up into the kidneys, and the flow of urine through the urethra helps to eliminate bacteria. Men, women, and children develop UTIs.

Types

Urinary tract infections usually develop first in the lower urinary tract (urethra, bladder) and, if not treated, progress to the upper urinary tract (ureters, kidneys). Bladder infection (cystitis) is by far the most common UTI. Infection of the urethra is called urethritis. Kidney infection (pyelonephritis) requires urgent treatment and can lead to reduced kidney function and possibly even death in untreated, severe cases.

Incidence and Prevalence

Approximately 8 to 10 million people in the United States develop a UTI each year. Women develop the condition much more often than men, for reasons that are not fully known, although the much shorter female urethra is suspected. The condition is rare in boys and young men.

Twenty percent of women in the United States develop a UTI and 20% of those have a recurrence. Urinary tract infections in children are more common in those under the age of 2.

Causes and Risk Factors

Escherichia coli (E. coli) causes about 80% of UTIs in adults. These bacteria are normally present in the colon and may enter the urethral opening from the skin around the anus and genitals. Women may be more susceptible to UTI because their urethral opening is near the source of bacteria (e.g., anus, vagina) and their urethra is shorter, providing bacteria easier access to the bladder. Other bacteria that cause urinary tract infections include Staphylococcus saprophyticus (5 to 15% of cases), Chlamydia trachomatis, and Mycoplasma hominis. Men and women infected with chlamydia trachomatis or mycoplasma hominis can transmit the bacteria to their partner during sexual intercourse, causing UTI.

Sexual intercourse triggers UTI in some women, for unknown reasons. Women who use a diaphragm develop infections more often, and condoms with spermicidal foam may cause the growth of E. coli in the vagina, which may enter the urethra.

Urinary catheterization (small tube inserted into the bladder through the urethra to drain urine) can also cause UTI by introducing bacteria into the urinary tract. The risk for developing a UTI increases when long-term catheterization is required.

In infants, bacteria from soiled diapers can enter the urethra and cause UTI. E. coli may also enter the urethral opening when young girls do not wipe from front to back after a bowel movement.

Other risk factors include the following:

  • Bladder outlet obstructions (e.g., kidney stones, BPH)
  • Conditions that cause incomplete bladder emptying (e.g., spinal cord injury)
  • Congenital (present at birth) abnormalities of the urinary tract (e.g., vasicoureteral reflux)
  • Suppressed immune system
  • Being uncircumcised

Certain blood types enable bacteria to attach more easily to cells that line the urinary tract, causing recurrent UTIs.