Urinary tract infections are a serious health problem affecting millions of people each year. Infections of the urinary tract are common - only respiratory infections occur more often. Each year, urinary tract infections (UTIs) account for about 8 million doctor visits. Women are especially prone to UTIs for reasons that are poorly understood. One woman in five develops a UTI during her lifetime.
Normal urine is sterile. It contains fluids, salts, and waste products, but it is free of bacteria, viruses, and fungi. An infection occurs when microorganisms, usually bacteria from the digestive tract, cling to the opening of the urethra and begin to multiply. Most infections arise from one type of bacteria, Escherichia coli(E. coli), which normally live in the colon.
In most cases, bacteria first begin growing in the urethra. An infection limited to the urethra is called urethritis. From there bacteria often move on to the bladder, causing a bladder infection (cystitis). If the infection is not treated promptly, bacteria may then go up the ureters to infect the kidneys (pyelonephritis).
Microorganisms called Chlamydia and Mycoplasma may also cause UTIs in both men and women, but these infections tend to remain limited to the urethra and reproductive system. Unlike E. coli, Chlamydia and Mycoplasma may be sexually transmitted, and infections require treatment of both partners.
The urinary system is structured in a way that helps ward off infection. The ureters and bladder normally prevent urine from backing up toward the kidneys, and the flow of urine from the bladder helps wash bacteria out of the body. In men, the prostate gland produces secretions that slow bacterial growth. In both sexes, immune defenses also prevent infection. Despite these safeguards, though, infections still occur.
Scientists are not sure why women have more urinary infections than men. Some people are more prone to getting a UTI than others. Any abnormality of the urinary tract that obstructs the flow of urine (a kidney stone, for example) sets the stage for an infection. An enlarged prostate gland also can slow the flow of urine, thus raising the risk of infection.
A common source of infection is catheters, or tubes, placed in the bladder. A person who cannot void, is unconscious, or is critically ill, often needs a catheter that stays in place for a long time. Some people, especially the elderly or those with nervous system disorders who lose bladder control, may need a catheter for life. Bacteria on the catheter can infect the bladder, so hospital staff take special care to keep the catheter sterile and remove it as soon as possible.
People with diabetes have a higher risk of a UTI because of changes in the immune system. Any disorder that suppresses the immune system raises the risk of a urinary infection.
UTIs may occur in infants who are born with abnormalities of the urinary tract that sometimes need to be corrected with surgery. UTIs are rarely seen in boys and young men. In women, though, the rate of UTIs gradually increases with age. Scientists are not sure why women have more urinary infections than men. One factor may be that a woman's urethra is short, allowing bacteria quick access to the bladder. Also, a woman's urethral opening is near sources of bacteria from the anus and vagina. For many women, sexual intercourse seems to trigger an infection, although the reasons for this linkage are unclear.
According to several studies, women who use a diaphragm are more likely to develop a UTI than women who use other forms of birth control. Recently, researchers found that women whose partners use a condom with spermicidal foam also tend to have growth of E. coli bacteria in the vagina.
Many women suffer from frequent UTIs. Nearly 20 percent of women who have a UTI will have another, and 30 percent of those will have yet another. Of the last group, 80 percent will have recurrences.
Usually, the latest infection stems from a strain or type of bacteria that is different from the infection before it, indicating a separate infection. (Even when several UTIs in a row are due to E. coli, slight differences in the bacteria indicate distinct infections.)
Research funded by the National Institutes of Health (NIH) suggests that one factor behind recurrent UTIs may be the ability of bacteria to attach to cells lining the urinary tract. A recent NIH-funded study has also shown that women with recurrent UTIs tend to have certain blood types. Some scientists speculate that women with these blood types are more prone to UTIs because the cells lining the vagina and urethra may allow bacteria to attach more easily. Further research will show whether this association is sound and proves useful in identifying women at high risk for UTIs.