Also Known As
UTI
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This article waslast modified on October 10, 2017.
What is a urinary tract infection?

A urinary tract infection (UTI) is an infection in one or more structures in the urinary tract. The urinary tract consists of two kidneys, two ureters, a bladder, and a urethra

The kidneys are bean-shaped organs found in the lower back below the ribcage. They filter waste out of the blood and produce urine to carry waste and excess water out of the body. Urine flows from the kidneys through the ureters and into the bladder.

The bladder is a hollow, muscular organ that stores urine for a short period of time. The bladder stretches as urine accumulates and, at a certain point, it signals the body to relieve the growing pressure. A muscular valve at the opening of the bladder relaxes and the bladder contracts to send urine through the urethra and out of the body.

The blanket term UTI is frequently used, but a urinary tract infection may also be identified by the specific part of the urinary tract that is affected.

  • Urethritis is an inflammation and/or infection of the urethra.
  • A bladder infection is called cystitis.
  • Infection of one or both kidneys is called pyelonephritis.


Urine does not normally contain microbes. Urinary tract infections develop when bacteria enter the opening of the urethra. The bacteria stick to the walls of the urethra, multiplying and moving up the urethra to the bladder. Most UTIs remain in the lower urinary tract (urethra or bladder), where they cause symptoms such as urinary urgency and a burning sensation during urination. Typically, these infections are considered uncomplicated and are easily treated, but if they are not addressed, the infection may spread through the ureters and into the kidneys.

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

Although a variety of bacteria can cause UTIs, most are due to Escherichia 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.

Urethritis may be a symptom of a sexually transmitted disease (STD) such as herpes, chlamydia, or gonorrhea. The treatment and prevention of STDs differs from that of typical UTIs. For more information, see the Sexually Transmitted Diseases article.

Urinary tract infections are common. According to the American Urological Association Foundation, UTIs result in more than 8.1 million visits to doctor's offices each year. Although they can affect anyone at any age, women are much more likely than men to have UTIs, with about 40% of women and 12% of men having at least one UTI in their lifetime.

It is thought that a woman's increased susceptibility is partly anatomical because the female urethra is relatively short compared to a male's, so bacteria do not have as far to travel to reach the bladder. Additionally, the short distance between the female urethra and the vagina and anus increases the risk of exposure to bacteria.

Anything that slows or blocks the passage of the urine or introduces bacteria into the urinary tract can increase a person's risk of having a UTI. Activities and conditions that can lead to the development of UTIs include:

  • Sexual intercourse with the same, new or multiple sex partners
  • Spermicide use, especially if combined with diaphragm or condom use
  • A history of previous UTIs 
  • Anatomical problems, such as narrowing of the 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
  • Spinal cord injuries or other nerve damage involving the bladder
  • Diabetes, which causes changes to the immune system, damage to the kidneys, and often results in glucose (sugar) in the urine that promotes the growth of bacteria
  • Kidney disease or kidney transplant
  • Any condition that suppresses the immune system
  • In men, an enlarged prostate, which may reduce the flow of urine
  • In women, menopause leads to changes in the lining of the vagina and the loss of the protective effects of estrogen


In most cases, UTIs are acute and uncomplicated. They are treated and the symptoms subside within a day or two. UTIs that spread to the kidneys, however, may cause permanent kidney damage, especially in the elderly or very young. Conditions or diseases that result in chronic or recurrent UTIs may also damage the kidneys and, in some cases, cause renal failure and septicemia, which can be life-threatening conditions. They require immediate treatment, which often involves hospitalization. In pregnant women, UTIs can lead to premature labor and delivery and cause high blood pressure. In men, UTIs can cause prostate infection and inflammation, which can be difficult to treat.

Recurrent UTIs are a problem for about 1 in 5 women after having their first infection. Most recurrent UTIs are caused by the same bacteria that caused previous infections. With each UTI a woman has, her risk of continuing to have more increases. Risk factors for recurrent UTIs in women include:

  • Frequent sexual intercourse
  • Having a first UTI at an early age
  • Spermicide use
  • Having a maternal history of UTIs


Men are less likely than women to have a first UTI. But once a man has a UTI, he is likely to have another because bacteria can hide deep inside prostate tissue.

Accordion Title
About Urinary Tract Infections
  • Signs and Symptoms

    Although UTI symptoms vary, many people will experience:

    • More frequent urge to urinate or waking up at night to urinate, often with only a small amount of urine released
    • Pain or burning during urination
    • Cloudy, strong-smelling urine
    • Pelvic pain


    Those with UTIs may also have pressure in the lower abdomen and small amounts of blood in the urine. If the UTI is more severe and/or has spread into the kidneys, it may cause flank pain, high fever, shaking, chills, nausea or vomiting. Fevers are also seen when the infection spreads into the blood (septicemia, which can lead to sepsis).

  • Tests

    Common laboratory tests for urinary tract infections (UTIs) include:

    • Urinalysis—most UTIs are detected by performing a urinalysis, which looks for evidence of infection, such as bacteria and white blood cells in a sample of urine.
    • Urine culture—for people who have recurring UTIs and those who are hospitalized, urinalysis results are confirmed with a urine culture.
    • Susceptibility testing—this is done if there are microbes identified by the culture to determine which antibiotics will inhibit the growth of the bacteria or yeast causing the infection. The results will help a healthcare practitioner determine which drugs are likely to be most effective in treating a person's UTI.


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


    Non-laboratory Tests
    Imaging scans and special X-rays may be used to look for anatomical problems and/or signs of an underlying disease or condition that could be causing recurrent UTIs. Imaging tests are most often ordered for children with urinary tract infections (especially boys), adults with frequent or recurrent UTIs, and those who have blood in their urine. Each of the following imaging test provides different information about the structures of the urinary tract.

    • Kidney and bladder ultrasound – sound waves are used to produce images of the bladder and kidneys so the healthcare practitioner can see any structural abnormalities.
    • 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 – several types of scans may be used to examine the function and shape of the bladder and kidneys. For each scan type, a radioactive dye is injected into a vein. The dye is carried to the bladder and kidney, allowing the visualization of any structural abnormalities.
    • Cystoscopy – a flexible tube about the diameter of a straw is threaded up 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 abnormalities. 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.
    • Intravenous pyelogram (IVP) – used to look at the whole urinary tract; an opaque dye is injected into a vein, which then travels to the kidney and bladder. A series of x-rays are taken, which may reveal obstructions or structural abnormalities.
  • Treatment

    Most uncomplicated UTIs (those that occur in healthy people with normal, unobstructed urinary tracts) are treated with a 3-day to 5-day course of antibiotics. 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 the entire course of medication is taken as prescribed to ensure that all the bacteria are destroyed and reduce the risk of recurrent infection.

    Women who have recurrent UTIs may wish to discuss the following treatment options with their healthcare provider:

    • A long course (6 months or more) of low-dose antibiotics
    • A single dose of 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 the healthcare provider will need to select one or more antibiotics that will kill all of the bacteria causing the infection. If the infection has spread to the kidneys, the affected person may require several months of treatment. This is also true of men with prostate infections.

    Complicated UTIs include those that occur in people who have structural or functional abnormalities of the urinary tract, men and boys, people with diabetes and other chronic conditions, and pregnant women. Complicated UTIs usually require a longer course of antibiotics, starting 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. Kidney infection is often treated as a complicated UTI.

    Sometimes recurrent or chronic UTIs will occur until an underlying structural abnormality, stone, obstruction, or disease or condition is addressed. For some conditions, surgery may be required to correct the underlying problem.

  • Prevention

    Once a person has had a urinary tract infection (UTI), there are actions that can be taken to prevent recurrences.

    • Frequent sexual intercourse is associated with recurrent UTIs in young women. Staying well hydrated and 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. Individuals may wish to consult their healthcare provider about alternative methods of birth control.
    • Women who are prone to UTIs may wish to ask their healthcare provider to prescribe an antibiotic to be taken immediately before or after sex.
    • Postmenopausal women may benefit from the use of topical estrogen and probiotics. Topical estrogen normalizes vaginal pH, which will help support the growth of lactobacilli or "good bacteria." The lactobacilli in probiotics can then colonize the vagina and prevent the overgrowth of bacteria that can cause UTIs.
    • 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.
    • Urinary tract infections occur when bacteria from the anus enter the urethra. This can occur when a person is constipated or has diarrhea and does not wipe themselves properly, so maintaining regularity can be an important factor in preventing UTIs.
    • Cranberry juice and cranberry supplements have unproven benefit in reducing urinary tract infections. Most studies have shown that cranberry juice and supplements don't contain enough of the active ingredient that can keep UTI-causing bacteria from sticking to the urinary tract. Cranberry supplements appear to be most effective in younger women.
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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used. To access online sources, copy and paste the URL into your browser.

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