Also Known As
UTI
Bladder Infection
Kidney Infection
Cystitis
Pyelonephritis
Urethritis
This article was last reviewed on
This article waslast modified on March 27, 2020.
What is a urinary tract infection?

A urinary tract infection (UTI) occurs when bacteria or sometimes other microbes enter the urinary tract and begin to grow, usually causing signs and symptoms such as pain and inflammation.

The urinary tract consists of two kidneys, two ureters, a bladder, and a urethra. The kidneys are bean-shaped organs located at the bottom of the ribcage to the right and left of the spine. They filter waste out of the blood and produce urine, which carries the waste and excess water out of the body.

Urine flows from the kidneys through narrow tubes called ureters and into the bladder. The bladder stores urine for a short period of time, but as urine collects, you eventually feel the need to urinate and the bladder contracts to send urine through another tube called the urethra and out of the body.

Urine normally contains very few or no bacteria or other microbes. However, bacteria can sometimes enter the opening of the urethra, multiplying and moving up the urethra to the bladder, causing an infection. Most UTIs remain in the lower urinary tract (urethra or bladder), where they cause symptoms such as a frequent urge to urinate and a burning sensation during urination. Typically, these infections are considered uncomplicated and are easily treated. Left untreated, the infection may spread to the kidneys.

A bladder infection is the most common type of UTI, but other parts of the urinary tract can become infected. These infections may also be identified by the specific part of the urinary tract that is affected:

  • Inflammation and/or infection of the urethra is called urethritis.
  • A bladder infection is called cystitis.
  • Infection of one or both kidneys is called pyelonephritis.

A kidney infection is more serious than a lower urinary tract infection and can lead to permanent kidney damage. In some cases, a UTI may spread to the bloodstream (septicemia) and may lead to sepsis, which can be life-threatening. Rarely, a bloodstream infection that originated elsewhere in the body may infect the kidneys.

Urinary tract infections are common. According to the American Urological Association (AUA), UTIs result in more than 8.1 million healthcare practitioner visits each year. Although UTIs can affect anyone at any age, women of all ages and men over 50 years of age are the most likely to get a UTI.

Children can also develop UTIs, though less commonly than in adults. Up to 8% of girls and 2% of boys will get UTIs, according to the AUA. Young children have a higher risk of kidney damage related to UTIs compared to older children and adults.

Accordion Title
About Urinary Tract Infections
  • Causes

    Although a variety of bacteria can cause UTIs, most are due to Escherichia coli (E. coli), bacteria that are common in the digestive system and are routinely found in stool and around the anus. Other bacteria that may cause UTIs include species of Proteus, Klebsiella, Enterococcus, and Staphylococcus. Occasionally, UTIs may be caused by a fungus (yeast), such as Candida albicans.

    Inflammation and infection of the urethra (urethritis) may be caused by sexually transmitted diseases (STDs) such as herpes, chlamydia, or gonorrhea. The treatment and prevention of STDs differs from that of typical UTIs and are not addressed in this article. For more information, see the Sexually Transmitted Diseases article.

  • Risk

    Women are more likely to get UTIs than men. About 60% of women and 12% of men will have at least one UTI in their lifetime. The increase in women is because they have shorter urethras than men and bacteria and other microbes spread more easily up the female urethra to the bladder. Also, the short distance between a woman’s urethra and anus also increases the risk of microbes spreading to the urinary tract. In men, as they age, the prostate gland may enlarge and lead to incomplete bladder emptying, which can increase the risk of UTIs.

    Anything that slows or blocks the flow of urine or introduces bacteria into the urinary tract can increase your risk of having a UTI. Examples of activities, factors and conditions that can lead to UTIs include:

    • Sexual intercourse, especially in younger women
    • Spermicide use, especially if combined with diaphragm or condom use
    • Wiping from back to front after a bowel movement in women
    • Holding urine when you feel the need to urinate
    • Having previous UTIs
    • Anatomical problems, such as narrowing of the tubes that urine passes through (urethra or ureters)
    • Urine retention (the bladder does not empty completely)
    • Abnormal flow of urine from the bladder back to the ureters (vesicoureteral reflux)
    • Kidney stones
    • Bladder catheterization, especially long-term (a bladder catheter is a long, thin, flexible tube that is inserted through the opening of the urethra and into the bladder to allow the passage of urine out of the body)
    • Spinal cord injuries or nerve damage involving the bladder
    • Diabetes, which can affect the immune system, cause kidney damage, and often results in glucose (sugar) in the urine that promotes the growth of bacteria and yeast; some medications used to treat diabetes can lead to increased glucose in the urine, which raises the risk of UTIs.
    • Kidney disease or kidney transplant
    • Any condition that suppresses the immune system
    • Menopausal changes in women, such as thinning of the vaginal lining and a decline in the hormone estrogen, can make them more prone to UTIs.
  • Complications and Repeated UTIs
    • Left untreated, infections of the lower urinary tract can spread to the kidneys and may cause permanent kidney damage, especially in the elderly or very young children.
    • Long-lasting or repeated UTIs may also damage the kidneys and, in some cases, cause renal failure.
    • Sometimes UTIs can spread to the blood (septicemia), leading to sepsis, which can be life-threatening. These cases require immediate treatment, which often involves hospitalization.
    • In pregnant women, UTIs can lead to premature labor and delivery and cause high blood pressure (preeclampsia).
    • Repeated UTIs are a problem for 20% to 40% of women after having their first infection.
    • UTIs are rare in men younger than 50 years of age but may occur with STDs, in uncircumcised men, with an abnormal narrowing of the urethra, and after anal intercourse. As men age, they are more likely to experience their first UTI and then are more likely to have repeat UTIs. The bacteria may also infect the prostate and be difficult to treat. The prostate is a small gland that encircles the upper urethra in men.
  • Signs and Symptoms

    UTI symptoms can vary, but typical signs and symptoms include:

    • More frequent urge to urinate, often with only a small amount of urine released
    • Pain or burning during urination
    • Cloudy, strong-smelling urine
    • Urine that appears red, bright pink, or cola-colored
    • Pain in the lower abdomen or pelvis

    If the UTI is more severe and/or has spread into the kidneys, it may cause pain in the mid-back below the ribs and above the pelvis (flank pain), high fever, shaking, chills, nausea, and/or vomiting. Fevers are also seen when the infection spreads into the blood (septicemia, which can lead to sepsis).

    Infants and young children who can't tell you how they feel may have only vague signs when they have a UTI. They may seem fussy or generally unwell, not eat or have a fever. Urine in their diaper may smell bad. If you child has a fever and is sick without an obvious reason, contact their pediatrician.

  • Testing

    Laboratory tests are performed to diagnose UTIs and sometimes to identify the bacteria (or other microbes) that is causing the infection as well as the treatment to cure the infection.

    Common laboratory tests for UTIs include:

    • Urinalysis—most UTIs are diagnosed by performing a urinalysis, which looks for evidence of infection, such as bacteria and white blood cells in a sample of urine. A positive leukocyte esterase test or the presence of nitrite in the urine supports the diagnosis of UTI.
    • Urine culture—identifies the specific microbe causing the infection. A culture is not always performed. If it is a first, uncomplicated UTI of the lower urinary tract, the healthcare practitioner may assume that it is caused by the most common microbe (E. coli) and will treat it without performing a culture. However, a culture may be done to confirm a positive urinalysis in certain cases, such as people with recurring UTIs or hospitalized patients.
    • Susceptibility testing—if the urine culture is positive, this testing may be done to determine which antimicrobial drug (antibiotic or antifungal) is most likely to be effective in treating your UTI.

    One or more laboratory tests may be done as follow up in certain cases:

    Non-laboratory Tests
    If you have frequent UTIs, imaging scans and special X-rays may be helpful in looking for urinary tract structural problems or blockages and/or signs of an underlying disease or condition. Imaging tests are most often ordered for children with urinary tract infections (especially boys), adults with frequent or recurrent UTIs, and people with blood in their urine.

    Some examples of these imaging tests include:

    • Kidney and bladder ultrasound—sound waves are used to produce images of the bladder and kidneys.
    • Voiding cystourethrogram (VCUG)—an imaging technique that allows the urethra and bladder to be viewed in real-time while the bladder fills and empties.
    • Nuclear scans—a radioactive dye is injected into a vein; the dye is carried to the bladder and kidneys and may show structural defects or blockages.
    • Cystoscopy—a flexible tube is threaded through the urethra and into the bladder. It allows a healthcare practitioner to look at the inner lining of the urethra and bladder. It can help identify blockages and defects. If a stone is present, other instruments can be inserted through the cystoscope that may allow a stone to be removed or broken into smaller pieces with a laser. Urine and tissue samples can also be obtained using the cystoscope.
    • Urography using intravenous pyelogram (IVP), computed tomography (CT) or magnetic resonance imaging (MRI)—used to look at the whole urinary tract; a contrast material is injected into a vein and then travels to the kidney and bladder. The x-rays (IVP) or scans may reveal obstructions or structural defects.

    For more information on these see RadiologyInfo's web pages on Hematuria, Kidney and Bladder Stones, or Kidney (Renal) Failure.

  • Prevention

    Once you've had a urinary tract infection (UTI), there are steps you can take to prevent another one:

    • Use the bathroom as soon as you feel the urge to urinate. Don’t hold urine in.
    • Drink plenty of fluids each day. This will dilute the urine and keep it moving through the urinary tract, making it more difficult for bacteria to adhere to the walls of the urethra and bladder.
    • Sexual intercourse is associated with recurrent UTIs, especially in younger women. Urinating after sex may help prevent UTIs. Avoiding the use of spermicidal foams and jellies, products (such as condoms) containing spermicides, and barrier methods of birth control (such as diaphragms) may reduce the frequency of UTIs. Talk to your healthcare practitioner about other birth control methods that are less likely to cause UTIs.
    • Postmenopausal women may benefit from the use of vaginal estrogen gels or creams.
    • In women, UTIs may occur when bacteria from the anus enter the urethra. To lower the risk of this, be sure to wipe from front to back after a bowel movement.
    • Some people drink cranberry juice or take cranberry supplements to prevent UTIs, but studies on this have not been conclusive. You may choose to drink cranberry juice or take cranberry supplements if you find it helpful and it won't cause harm. However, people with diabetes should avoid sugary drinks.
  • Treatment

    If you are otherwise healthy (i.e., have a normal, unobstructed urinary tract) and have an uncomplicated UTI, you will typically be treated with antibiotics for three to five days. Symptoms such as pain and a frequent urge to urinate usually resolve after a day or two of antibiotic treatment. However, it is important that you take the full course of antibiotics to ensure that your infection is cured and to reduce the risk of recurrent infection.

    Women with recurrent UTIs may wish to discuss the following treatment options with their healthcare practitioner:

    • A long course (6 months or more) of low-dose antibiotics
    • A single dose of an antibiotic after sexual intercourse
    • Vaginal estrogen therapy for postmenopausal women

    In a complicated or recurrent UTI, the infection may be caused by more than one type of bacteria and your healthcare practitioner will need to select one or more antibiotics that will kill all of the bacteria causing the infection. Complicated UTIs usually require a longer course of antibiotics and may start with intravenous (IV) antibiotic therapy in in the hospital. After a short period of IV antibiotics, the antibiotics are given by mouth for up to several weeks.

    If the infection has spread to your kidneys, it will likely be treated as a complicated UTI and you may require several months of treatment. This is also true of men with prostate infections.

    Complicated UTIs include can occur in:

    • People with defects in the structure or function of their urinary tract; this is a common cause of UTI in boys and young men, and occasionally occurs in girls and women.
    • Older men with prostate enlargement
    • People with diabetes and other chronic conditions
    • Pregnant women—UTIs can put the mother and baby at risk if not treated promptly

    Sometimes UTIs will continue to recur or be long-lasting until an underlying structural defect, kidney stone, obstruction, or disease or condition is addressed. For some conditions, surgery may be required to correct the underlying problem.

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