What causes a urinary tract infection?
The urine is normally sterile. An infection occurs when bacteria get into the urine and begin to grow. The infection usually starts at the opening of the urethra where the urine leaves the body and moves upward into the urinary tract.
- The culprit in at least 90% of uncomplicated infections is a type of bacteria called Escherichia coli, better know as E. coli. These bacteria normally live in the bowel (colon) and around the anus.
- These bacteria can move from the area around the anus to the opening of the urethra. The two most common causes of this are improper wiping and sexual intercourse.
- Usually, the act of emptying the bladder (urinating) flushes the bacteria out of the urethra. If there are too many bacteria, urinating may not stop their spread.
- The bacteria can travel up the urethra to the bladder, where they can grow and cause an infection.
- The infection can spread further as the bacteria move up from the bladder via the ureters.
- If they reach the kidney, they can cause a kidney infection (pyelonephritis), which can become a very serious condition if not treated promptly.
The following people are at increased risk of urinary tract infection:
- People with conditions that block (obstruct) the urinary tract, such as kidney stones
- People with medical conditions that cause incomplete bladder emptying (for example, spinal cord injury or bladder decompensation after menopause)
- People with suppressed immune systems: Examples of situations in which the immune system is suppressed are HIV/AIDS and diabetes. People who take immunosuppressant medications such as chemotherapy for cancer also are at increased risk.
- Women who are sexually active: Sexual intercourse can introduce larger numbers of bacteria into the bladder. Urinating after intercourse seems to decrease the likelihood of developing a urinary tract infection.
- Women who use a diaphragm for birth control
- Men with an enlarged prostate: Prostatitis or obstruction of the urethra by an enlarged prostate can lead to incomplete bladder emptying, thus increasing the risk of infection. This is most common in older men.
- Males are also less likely to develop UTIs because their urethra (tube from the bladder) is longer. There is a drier environment where a man's urethra meets the outside world, and fluid produced in the prostate can fight bacteria.
- Breastfeeding has been found to decrease the risk for urinary tract infections in children.
The following special groups may be at increased risk of urinary tract infection:
- Very young infants: Bacteria gain entry to the urinary tract via the bloodstream from other sites in the body.
- Young children: Young children have trouble wiping themselves and washing their hands well after a bowel movement. Poor hygiene has been linked to an increased frequency of urinary tract infections.
- Children of all ages: Urinary tract infection in children can be (but is not always) a sign of an abnormality in the urinary tract, usually a partial blockage. An example is a condition in which urine moves backward from the bladder up the ureters (vesicoureteral reflux).
- Hospitalized patients or nursing-home residents: Many of these individuals are catheterized for long periods and are thus vulnerable to infection of the urinary tract. Catheterization means that a thin tube (catheter) is placed in the urethra to drain urine from the bladder. This is done for people who have problems urinating or cannot reach a toilet to urinate on their own.
Related SlideshowUrinary Tract Infection
Are urinary tract infections contagious?
No. Urinary tract infections (UTIs) are not contagious.