Office of Women's Health

Facts About Urinary Tract Infections
What are the causes of urinary tract infections?

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 lives 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).

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, infections still occur.

Are women at a higher risk for UTIs?

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. 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. One woman in five develops a UTI during her lifetime.

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, which may increase the risk of a UTI.

Infections in Pregnancy
Pregnant women seem no more prone to UTIs than other women. However, when a UTI does occur, it is more likely to travel to the kidneys. According to some reports, about 2 to 4 percent of pregnant women develop a urinary infection. Scientists think that hormonal changes and shifts in the position of the urinary tract during pregnancy make it easier for bacteria to travel up the ureters to the kidneys. For this reason, many doctors recommend periodic testing of urine.

What are the Symptoms of UTI?

Not everyone with a UTI has symptoms, but most people have at least one. Symptons may include a frequent urge to urinate and a painful, burning feeling in the area of the bladder or urethra during urination. It is not unusual to feel bad all over—tired, shaky, washed out—and to feel pain even when not urinating. Often, women feel an uncomfortable pressure above the pubic bone, and some men experience a fullness in the rectum. It is common for a person with a urinary infection to complain that, despite the urge to urinate, only a small amount of urine is passed. The urine itself may look milky or cloudy, even reddish if blood is present. A fever may mean that the infection has reached the kidneys. Other symptoms of a kidney infection include pain in the back or side below the ribs, nausea or vomiting.

How is UTI Diagnosed?

To find out whether you have a UTI, your doctor will test a sample of urine for pus and bacteria. You will be asked to give a “clean catch” urine sample by washing the genital area and collecting a “midstream” sample of urine in a sterile container. This method of collecting urine helps prevent bacteria around the genital area from getting into the sample and confusing the test results.

How is UTI Treated?

UTIs are treated with antibacterial drugs. The choice of drug and length of treatment depends on the patient’s history and the urine tests that identify the offending bacteria. The sensitivity test is especially useful in helping the doctor select the most effective drug. Often a UTI can be cured with one or two days of treatment if the infection is not complicated by an obstruction or nervous system disorder. Still, many doctors ask their patients to take antibiotics for a week or two to ensure that the infection has been cured.

More information about urinary tract infections can be obtained by contacting:

National Institutes of Health, National Kidney and Urologic Diseases Information Clearinghouse