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Urinary Tract Infection (UTI)

Last Updated: Mar 1, 2019


A urinary tract infection, or UTI, is an infection of any part of the urinary system, the group of organs that removes water and waste products from the blood.

Lower urinary tract

About 95 percent of UTIs involve the lower urinary tract. This includes the bladder (the organ that collects and holds urine) and the urethra (the tube through which urine exits the body). Lower urinary tract infections are also called cystitis. They can be quite painful, but usually don’t cause permanent damage.

Sometimes cystitis spreads to the upper urinary tract, causing a more serious infection called pyelonephritis. This can affect the kidneys (the organs that remove excess water and waste products from the blood) and the ureters (the tubes that connect the kidneys and bladder). In acute (sudden, short-term) pyelonephritis, there is a risk that bacteria will enter the blood stream, causing a life-threatening condition called septicemia. Chronic (long-term) pyelonephritis can cause scarring and permanent damage to the kidneys.

UTIs are four times more common in women than in men. This is because women have a shorter urethra, which allows bacteria to spread easily to the bladder. Also, for women the urethra is a shorter distance from the anus, a common source of infection.

While UTIs are less common in men, they tend to be more severe when they do occur.

Causes and Risk Factors

A UTI begins when disease-causing microorganisms enter the urinary tract through the urethra. Usually the body’s immune system can fight off these invaders, but if they multiply too quickly, they can overwhelm the body’s natural defenses. The most common cause of UTIs is bacteria called Escherichia coli (E. coli) that lives in the human bowel.

Bacteria often multiply in the urinary tract when a person doesn’t urinate frequently enough. (Urination washes bacteria out of the body.) Infrequent urination may be due to a medical condition such as a kidney stone or blockage or simply to personal habits.

Frequent sexual activity also contributes to the development of UTIs, especially for women. The friction of sexual intercourse can push bacteria into the urethra. Nearly 80 percent of UTIs in young women occur shortly after sexual intercourse. Women who use a diaphragm or spermicide for birth control are at especially high risk, as both encourage the growth of excess bacteria.

People with diabetes or conditions that suppress the immune system may have a harder time fighting off harmful bacteria and consequently may experience more UTIs.

Changes in estrogen levels at menopause thin the lining of the urinary tract, which creates small tears in which bacteria can grow.

Pregnant women are at increased risk for pyelonephritis, which increases the chances of premature birth and low birth weight for the baby.


Not all urinary tract infections cause symptoms. Those that don’t usually clear up on their own without treatment.

Common symptoms of cystitis include:

Additional symptoms of pyelonephritis include:


Upper urinary tract

Because of the risk of complications, it’s important to see a doctor promptly if you have signs of a UTI. In most cases your primary care doctor can effectively diagnose and treat this condition.

UTIs are usually diagnosed based on medical history and a lab test called urinalysis. During urinalysis, a urine sample is examined under a microscope to determine the presence of bacteria and white and red blood cells.

For severe or recurrent infections, the doctor may order a urine culture. This involves placing drops of urine into several different mediums. Each medium encourages the growth of a different bacterium. Within a few days, the lab can identify the bacteria causing the infection and test its sensitivity to various antibiotics.

Patients with recurrent UTIs may be referred to a urologist, a physician who specializes in treating diseases of the urinary tract. The urologist can perform imaging and mechanical tests to determine the underlying cause of the infections, including:


Urinary tract infections are treated with antibiotics, a class of medications that kill bacteria. The type of antibiotic prescribed depends on which bacteria cause the infection. Though most people feel better within one or two days of beginning antibiotics, it’s important to finish the entire course. In cases of severe infection, intravenous antibiotics may be administered at the hospital.

People with UTIs may also benefit from certain analgesics (pain killers) that numb the bladder and help make urination more comfortable. These are available both in prescription form and over the counter. Discolored urine is a common but harmless side effect.

Patients can also promote healing by drinking plenty of water and avoiding coffee, alcohol and other substances that irritate the bladder. Applying a warm heating pad to the stomach may help relieve abdominal pain.

In most cases, cystitis clears up completely following a course of antibiotics. However, recurrence is a problem. About one in five young women who has a UTI will have another within a year, and about 3-5 percent of women experience them several times a year. In men, disease-causing bacteria can “hide” in the prostate tissue, causing inflammation and recurring infections.


There are many steps you can take to reduce your risk of a UTI:


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Tina Shahian, PhD

Tina is a writer for Innerbody Research, where she has written a large body of informative guides about health conditions.


A communication specialist in life science and biotech subjects, Tina’s successful career is rooted in her ability to convey complex scientific topics to diverse audiences. Tina earned her PhD in Biochemistry from the University of California, San Francisco and her BS degree in Cell Biology from U.C. Davis. Tina Shahian’s Linkedin profile.


In her spare time, Tina enjoys drawing science-related cartoons.