Infection: Urinary Tract Infection

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Infection: Urinary Tract Infection

Causes and Symptoms
The Future
For more information


Urinary tract infections, or UTIs, are disorders caused by infections, mostly bacterial but sometimes fungal or viral, of the urinary bladder, the urethra, the ureters, or the kidneys themselves. Infection of the bladder by itself is called cystitis; infection that has moved upward to the kidneys from the bladder or ureters is called pyelonephritis. UTIs can be caused by several different types of bacteria, but the most common offenders are bacteria that live in the intestines and get into the urinary tract because of poor cleansing after using the toilet. Other organisms that may be involved in a UTI include those that cause herpes, gonorrhea, and other sexually transmitted diseases.


The human urinary tract is usually free of bacteria, as is the urine it produces. Bacterial infections usually start when bacteria from the outside of

the body enter through the urethra, a thin tube that connects the urinary bladder in the lower abdomen to the outside. The urethra in adult women is only about 1.5–2 inches (3.8–5.1 centimeters) long, whereas the adult male urethra is about 8 inches (20.3 centimeters) long. This difference helps to explain why adult women are the group at greatest risk of UTIs. Bacteria from the area around the anus or the vagina can enter the female urethra during sexual intercourse, or they can be introduced into the opening of the urethra by wiping from back to front after using the toilet. In men, bacteria are most likely to get into the urethra following surgery or insertion of a urinary catheter.

Once the bacteria have entered the body through the urethra, they travel upward into the bladder, a hollow muscular organ in the lower abdomen that collects and stores urine. In the bladder, the bacteria may cause an inflammation known as cystitis, which is characterized by pain on urination, a need to urinate frequently, and cloudy, bloody, or foul-smelling urine.

If the infection is not treated, it may spread upward past the bladder through the ureters into the kidneys. The ureters are two tubes about 10 inches (25.4 centimeters) long in human adults that connect the kidneys to the bladder. A bacterial infection of the kidneys is more serious than a bladder infection because of the possibility of long-term damage to the kidneys. Patients with pyelonephritis may experience vomiting,

severe pain in the abdomen, night sweats, and a high fever as well as painful urination.


UTIs are largely an adult disorder, although between 1 and 2 percent of children are affected by them. According to the American Urological Association, urinary tract infections are responsible for more than 7 million visits to doctors each year in the United States and about 5 percent of all visits to primary care doctors. About 40 percent of women and 12 percent of men will experience at least one UTI during their lifetime. Although UTIs are less common in boys and men than in girls and women, they are also more serious when they do occur.

UTIs in Children

Most people think of urinary tract infections (UTIs) as an adult problem, but between 1 and 2 percent of children develop UTIs. These can be serious, because small children are much more likely than older children or adults to suffer lasting kidney damage from UTIs, and children may be too young to tell an adult when and where they are having pain; they may have only a fever, smelly urine in a diaper, diarrhea, or no symptoms at all. It is best to take a small child to the doctor if he or she is running a high fever and there is no other obvious explanation for it such as an ear infection or a cold.

As with an adult, the diagnosis of a UTI in a small child is based on a urine sample. After the infection clears, the doctor may recommend additional tests to check for abnormalities in the structure of the child's ureters or urethra. In some cases children get recurrent UTIs because they are born with abnormally narrow passages in one or more parts of their urinary tract, which can prevent the normal passage of urine out of the body and encourage the growth of bacteria in the urine. Doctors usually recommend x-rays or other imaging studies for children with UTIs when the child is:

  • A girl over age five who has had two or more UTIs
  • A boy of any age who has his first UTI
  • Younger than five
  • Running a high fever

As far as is known, race or ethnicity does not affect a person's risk of UTIs. Factors that do increase risk, however, include:

  • Female sex. The female urethra is only a quarter as long as the male urethra, which makes it easier for bacteria to enter the female bladder.
  • Sexual activity. Sexual intercourse can irritate the opening of the urethra in women and allow bacteria to enter.
  • Pregnancy.
  • Age. Older men are more likely to develop UTIs because the swelling of the prostate gland may make it more difficult to empty the bladder completely. Women past menopause have an increased risk of UTIs because of the weakening of the muscles surrounding the bladder.
  • Women who use diaphragms as a method of birth control. The rigid frame on the outside of a diaphragm can irritate the urethra or put pressure on it.
  • People with diabetes.
  • People who have become dehydrated or are not drinking enough fluids.
  • People with anatomical abnormalities of the urinary tract.
  • People with a history of kidney stones.
  • People who have had surgery that requires the placement of a urinary catheter.

Causes and Symptoms

The cause of urinary tract infections is the introduction of bacteria into the urinary tract. If the bacteria are not washed out by urine, they may multiply in the tissues lining the urethra and the bladder, causing inflammation, fever, pus in the urine, and other symptoms of infection. It is possible for a person to have a UTI without noticeable symptoms of illness; however, most people will feel sick fairly rapidly after the infection begins.

The symptoms of a bladder infection include:

  • Burning or painful urination
  • A low fever (below 101°F/38.3°C)
  • Feeling a need to urinate frequently
  • Cloudy, bloody, or foul-smelling urine
  • Need to urinate at night
  • A feeling of pressure in the lower part of the pelvis

If the infection has spread to the kidneys, the patient may also have:

  • A high fever (over 101°F/38.3°C) and chills
  • Night sweats
  • Severe pain in the side around waist level or in the lower back
  • Nausea and vomiting
  • Mental confusion (more common in the elderly)


Diagnosis of a urinary tract infection is based on the patient's symptoms and the results of a urine test. Urine is usually obtained via a clean-catch midstream urine specimen: after cleansing the area around the urethral opening and urinating a small amount into the toilet, the patient then urinates into a small cup or container. If the patient is a small child or

an adult who cannot urinate, the doctor may obtain a sample by inserting a catheter into the bladder through the urethra.

The doctor can perform a simple urine test to determine whether an infection is present by looking for an increased number of white blood cells in the urine or for the bacteria themselves. To determine which specific bacterium is causing the infection, the doctor can send the urine sample to a laboratory for culture.

The doctor may order imaging tests if there is evidence that the infection is related to structural abnormalities in the patient's urinary tract. Imaging tests are most commonly ordered for patients who have recurrent UTIs (three or more in a year); young children with UTIs, particularly boys; and patients of any age who have blood in the urine.


Treatment of an uncomplicated urinary tract infection in most women is a three- to seven-day course of an antibiotic given by mouth. Adult males usually require two weeks of antibiotic treatment, and children are usually given a ten-day course of antibiotics. The doctor may also prescribe a medication that numbs the pain of urination while the infection is being treated. These drugs may discolor the urine either blue or bright orange.

If the patient has pyelonephritis, intravenous antibiotics may be needed, along with intravenous fluids if the patient is vomiting and cannot keep anything in the stomach. The patient will usually be given oral antibiotics for ten to fourteen days after the intravenous antibiotics are stopped. A patient who is very sick with pyelonephritis, is pregnant, or has kidney stones may be admitted to the hospital for treatment.

The doctor may recommend surgery for children or adults with anatomical abnormalities of the urinary tract in order to reduce the risk of recurrent UTIs and permanent damage to the kidneys.


Most people with uncomplicated cystitis recover in a few days without any long-term complications. About 1 percent of patients with pyelonephritis die following the spread of the infection from the kidneys to the bloodstream. Those most at risk of death from a severe urinary tract infection are the elderly, people with sickle cell anemia, people with cancer, and people with chronic kidney disease.


There are several precautions to reduce their risk of urinary tract infections:

  • Drink plenty of water and other fluids. There is some evidence that cranberry juice is particularly beneficial because it prevents bacteria from attaching to the cells of the tissues lining the bladder.
  • Empty the bladder regularly, particularly after sexual intercourse.
  • Women using the diaphragm as a method of birth control may wish to consider another method.
  • Cleanse the genital area from front to back after using the toilet. This helps to prevent bacteria from the area around the anus from getting into the urethra.
  • Urinate promptly when the bladder begins to feel full rather than holding in the urine for long periods of time. In addition, empty the bladder as completely as possible.
  • Avoid the use of deodorant sprays or other feminine hygiene products that can irritate the urethral opening; change tampons or napkins frequently during menstrual periods.
  • Wear underwear made of cotton rather than nylon or other synthetic fabrics.

In some cases the doctor may prescribe a low-dose antibiotic to be taken after sexual intercourse to prevent a urinary tract infection.

The Future

UTIs are likely to continue to be commonplace illnesses in the general population. Current research includes studies of electrochemical chips and other new technologies for rapid identification of the bacteria that cause UTIs.

SEE ALSO Diabetes


Bladder: A hollow organ in the lower abdomen that collects urine from the kidneys and stores it prior to urination.

Catheter: A thin tube inserted into the urethra to drain urine from the bladder.

Cystitis: The medical term for an infection of the urinary bladder.

Pyelonephritis: The medical term for a urinary tract infection that has spread from the bladder or other parts of the urinary tract upward to the kidneys.

Ureter: A muscular tube that carries urine from the kidney to the bladder.

Urethra: The thin tube that connects the bladder to the outside of the body.

Urologist: A doctor who specializes in diagnosing and treating disorders of the kidneys and urinary tract.

For more information


Litin, Scott C., ed. Mayo Clinic Family Health Book, 3rd ed. New York: HarperResource, 2003.


American Urological Association. Urinary Tract Infections in Adults. Available online at (updated December 2002; accessed July 15, 2008).

Mayo Clinic. Urinary Tract Infection. Available online at (updated June 27, 2008; accessed July 15, 2008).

National Institute of Child Health and Human Development (NICHD). Urinary Tract Infections (UTI). Available online at (updated August 25, 2006; accessed July 15, 2008).

National Institute of Diabetes and Digestive and Kidney Diseases. Urinary Tract Infections in Adults. Available online at (updated December 2005; accessed July 15, 2008).

TeensHealth. Urinary Tract Infections. Available online at (updated August 2006; accessed July 15, 2008).

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Infection: Urinary Tract Infection

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