Urinary Tract Infection

What is a urinary tract infection?

A urinary tract infection (UTI) is an infection of one or more components of 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 the wastes and excess water out of the body. The urine is carried from the kidneys, through the ureters, and into the bladder. The bladder is a hollow muscular organ that stores urine for a short period. The bladder stretches as urine accumulates and, at a certain point, it signals the body to relieve the growing pressure. A muscular sphincter valve at the opening of the bladder is relaxed 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 part of the urinary tract affected. Urethritis is an inflammation and/or infection of the urethra. Bladder involvement is called cystitis, and when one or more of the kidneys are inflamed or infected, it is called pyelonephritis.

Urine does not normally contain microorganisms, but if it is obstructed leaving the body or retained in the bladder, it provides a good environment for bacteria to grow. Most urinary tract infections are due to bacteria that are introduced into the opening of the urethra. They 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. Most of these infections are considered uncomplicated and are easily treated, but if they are not addressed, the infection may spread up through the ureters and into the kidneys. A kidney infection is more dangerous and can lead to permanent kidney damage. In some cases, a urinary tract infection 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, a bacterium that is common in the gastrointestinal tract and is routinely found in stool. Other bacteria that may cause UTIs include species of Proteus, Klebsiella, Enterococcus, and Staphylococcus. Occasionally, a UTI may be due to a yeast, such as Candida albicans; urethritis is often due to a sexually transmitted disease such as herpes, chlamydia, or gonorrhea.

Urinary tract infections are common. According to the American Urological Association Foundation, UTIs result in more than 7 million visits to doctor's offices a year. Although they can affect anyone at any age, women are much more likely than men to have a UTI with about 40% of women and 12% of men having at least one in their lifetime. It is thought that a woman's increased susceptibility is partly anatomical, because the woman's urethra is shorter and because their anus and vagina are relatively close to the urethra. Anything that slows down the passage of the urine, blocks it, or introduces bacteria into the urinary tract can raise a person's risk of having a UTI. Conditions that cause an increased risk for developing a UTI include:

• Anatomical problems, such as narrowing of the urethra or ureters
• Urine retention (the bladder does not empty completely)
• Vesicoureteral reflux (the abnormal flow of urine from the bladder back to the ureters)
• Kidney stones
• Bladder catheterization, especially long term
• Spinal cord injuries
• Diabetes - it causes changes to the immune system, damage to the kidneys, and often results in sugar in the urine, promoting the growth of bacteria
• Kidney disease
• Kidney transplant
• Any condition that suppresses the immune system
• In men, an enlarged prostate may inhibit the flow of urine.

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 and the very young. Conditions or diseases that result in chronic or recurrent UTIs may damage the kidneys and, in some cases, cause kidney failure. Renal failure and septicemia can be life-threatening conditions. They require immediate treatment, which often involves hospitalization. In pregnant women, a UTI can lead to premature labor and delivery and cause high blood pressure. In men, a UTI can cause prostate infection and inflammation, which can be difficult to treat.

Symptoms

Although UTI symptoms vary, many people will experience:

• A strong, persistent desire to urinate
• A burning sensation during urination
• A cloudy, strong-smelling urine
• Lower back 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 (sepsis). Some people may also experience mental changes and confusion with a UTI, while others may not have any symptoms at all.

Tests

Common Laboratory Tests
Most UTIs are detected by performing a urinalysis and then confirmed with a urine culture. If there are pathogenic bacteriapresent, then susceptibility testing is done to make sure that the antibiotic that the doctor chooses will effectively treat themicroorganism causing the infection.

• Urinalysis. A clean catch (midstream) sample collection is important to minimize sample contamination. White blood cells (WBC, leukocytes), red blood cells (RBC), nitrites, and bacteria in the urinalysis may indicate a UTI.
• Urine Culture. Urine is streaked on a thin layer of nutrient gel (agar plate), then incubated for 24-48 hours. Any bacteria that grow on the agar are counted and identified. Usually, if a person has a UTI, there will be a high colony count of one type of bacterium that will be present. If there are three or more types of bacteria present (or, in a woman, if there are vaginal bacteria such as lactobacillus or diphtheroids), then it is considered to be a contaminated sample and no further work is done on the culture. A repeat sample may need to be submitted if the person's symptoms persist. If there is a predominant growth of one type of bacterium present in high number, then susceptibility testing is done (sometimes the doctor may refer to it as "sensitivity" testing). The ability of different antibiotics to inhibit the growth of the bacteria in a test tube or on an agar plate helps predict which antibiotics are likely to be effective treatments.

Follow-up Laboratory Tests
If a doctor suspects that a UTI may have spread into the bloodstream, the doctor may order a blood culture. If a doctor suspects that a person's symptoms may be due to a sexually transmitted disease, such as chlamydia or gonorrhea, then the doctor may test for one or more STDs.

• Blood Culture. Two samples of blood are taken to look for any bacteria in the blood, which is normally sterile. The blood samples are incubated in a broth medium at body temperature and examined at regular intervals for bacterial growth. When a person is septic from a urinary tract infection, the same microorganism is found in both the blood and the urine cultures. Susceptibility testing will provide information on which antibiotic is likely to eradicate the pathogen from both the blood and the urine.

In the case of recurrent or chronic urinary tract infections, other laboratory tests such as glucose (to check for diabetes) or BUNand creatinine (to evaluate kidney function) may also be done.

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. If a person has recurrent or chronic UTIs, one or more of the following procedures may be ordered. Each gives the doctor different information.

• Kidney and bladder ultrasound – uses sound waves to determine the structures of the bladder and the kidney; they can be seen as light and shadowed areas.
• Voiding cystourethrogram (VCUG) – an x-ray test that examines the urethra and bladder while the bladder fills and empties
• Nuclear scans – several types 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 doctor to look at the surface of the inside of urethra and bladder. It can help identify blockages and abnormalities. If a stone is present, other instruments can be inserted up through the cystoscope that may allow a stone to be removed or broken into smaller pieces with a laser. The crushing of these stones is called lithotripsy. Urine and tissue sample can also be taken using the cystoscope.
• Intravenous pyelogram (IVP) – used to look at the whole urinary tract. An opaque dye is injected into a vein, then travels to the kidney and bladder. A series of x-rays are taken, which may reveal obstructions or structural abnormalities.

Prevention

Prevention of a UTI centers on keeping the urine moving through the urinary tract and avoiding bacterial contamination of theurethra. Recommendations include:

• Drink plenty of water every day to flush out the urinary system.
• Urinate as needed; don't hold urine in for extended periods of time.
• After a bowel movement, wipe from front to back to keep stool bacteria away from the urethra.
• Avoid irritants to the urethra – avoid bubble baths if prone to recurrent UTIs, take showers instead of baths, and rinse soap off thoroughly.
• Urinate after sexual intercourse; this may help rinse out any bacteria that may have come in contact with the urethra.
• Avoid tight clothing and wear cotton underwear; it breathes and won't trap moisture like some synthetic fibers.
• Drink cranberry juice – some doctors recommend this to their patients; it may help prevent bacteria from sticking to the walls of the urethra.

Treatment

A UTI is usually treated with a course of antibiotics. The type, concentration, and length of drug therapy will depend on:

• Which specific bacteria is/are present
• What drugs the bacteria is/are susceptible to
• How much of the urinary tract is involved
• The health/allergies of the infected person
• Whether or not the person is having recurrent UTIs
• Whether the infection is acute or chronic
• Whether the antimicrobial is being used as a preventive measure or to treat an existing infection
• Whether the infection has spread to the blood

In a complicated or recurrent UTI, the infection may be due to more than one bacterium and the doctor will need to select an antimicrobial or a combination of antibiotics that will treat 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 if the person is a male whose prostate has become infected.

If someone is particularly prone to recurrent infections and/or particularly vulnerable to kidney damage, his or her doctor may recommend preventive antimicrobials, either on a continuing basis or during times of increased risk.

If an infection is due to a sexually transmitted disease, such as chlamydia or gonorrhea, the doctor will prescribe specific drugs that have been proven to be effective against these organisms. If a person is sexually active and experiencing recurrent UTIs, it may be due to an asymptomatic infection in his or her partner. In some cases, both partners will need to be treated. If a woman is on oral contraceptives, she may want to talk to her doctor as some antimicrobials can lessen their effectiveness.

If a woman is on antimicrobial therapy for several days, there is a chance that she may develop diarrhea or a vaginal yeast infection. This is because the drugs also kill good/normal bacteria and upset the balance of bacteria in the body. If this happens, additional treatment may be required.

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.

Related Pages

On This Site
Tests: Urinalysis, Urine Culture, Blood Culture, Chlamydia, Gonorrhea, Kidney Stone Analysis, Susceptibility Testing
Conditions: Kidney Disease

Elsewhere On The Web
FamilyDoctor.org: Urinary Tract Infections 
KidsHealth.org: Urinary Tract Infections
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) 
NIDDK: Your Urinary System and How it Works
UrologyHealth.org: Urinary Tract Infections in Adults

Article Sources

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.

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