Understanding UTI

Urinary tract infections are a serious health problem affecting millions of people each year.

The urinary tract is a vital, finely balanced system whose task is to extract and dispose of the body's liquid wastes. Infections of the urinary tract are among the most common in the human body--so common that only respiratory infections occur more often. Each year, patients with symptoms of a urinary tract infection (UTI) account for 5 million visits to a doctor's office. Among women, UTI's are especially troublesome; it is estimated that up to 20 percent of women develop a UTI sometime in their lives.

The urinary system, made up of the kidneys, ureters, bladder, and urethra, eliminates liquid waste products and helps maintain a stable balance of salts and other dissolved substances in the blood. The key players in the system are the kidneys, a pair of purplish-brown organs located below the ribs toward the middle of the back. These highly complex organs remove liquid waste material from the bloodstream in the form of urine and produce a hormone that regulates the formation of red blood cells. Two narrow tubes called ureters carry urine from the kidneys to the bladder, a triangle-shaped chamber in the lower abdomen. Urine is stored in the bladder and emptied through another passageway, the urethra.

The average adult passes about 1,500 milliliters (about a quart and a half) of urine each day. The amount of urine varies, depending on the amount and type of food and fluids consumed. The volume formed at night is about half as much as that formed in the daytime.

Causes

Normal urine is sterile. It contains fluids, salts, and waste products, but it is free of microorganisms such as bacteria, viruses, or fungi. An infection occurs when microorganisms, usually bacteria from the digestive tract, adhere to the opening of the urethra and begin to multiply. Most infections can be traced to one type of colon bacteria, called Escherichia coli.

Recently, microorganisms called Chlamydia and Mycoplasma have been found to cause urinary tract infections in both men and women, but these tend to remain limited to the urethra and genital system. Unlike the majority of UTI' s, infections caused by these two microbes are sexually transmitted, are not detected by standard culturing methods, and require treatment of both sexual partners.

As they reproduce, bacteria colonize the urethra. An infection that is limited to the urethra is called urethritis. Often the bacteria migrate from the urethra to the bladder, causing cystitis (a bladder infection). It is important to treat the infection promptly, before bacteria that invade the lower urinary tract have a chance to travel upward, causing a kidney infection (pyelonephritis) and possibly kidney damage.

The urinary system is structured in a way that helps guard against infection. For instance, the ureters normally prevent the backup of urine toward the kidneys, and the flow of urine from the bladder helps wash harmful bacteria out of the body. In men, the prostate gland produces secretions that kill or inhibit infection-causing bacteria. In both sexes, various immune defenses also play a role in keeping infection at bay. Despite these and other safeguards, infections still occur. Scientists are not sure why women have more urinary infections than men.

Risk Factors Some people are more prone to getting a urinary infection than others. Any abnormality of the urinary tract that obstructs or slows the flow of urine makes it easier for bacteria to grow. When the urine does not empty freely, it may stagnate in the bladder. A stone in the kidney or any part of the urinary tract can form such a blockage, creating the conditions for a UTI. In men, an enlarged prostate gland can obstruct urine flow and make infection difficult to treat.

One of the most common sources of infection is catheters, or tubes, placed in the bladder. Patients who cannot void, are unconscious, or critically ill, often need a catheter that remains in place for a period of time. Because of the risk that bacteria inhabiting the catheter can enter and infect the bladder, hospital staff take special care to prevent the catheter from becoming contaminated. Also, physicians try to remove the catheter as soon as possible. Some patients, especially the elderly or those with diseases of the nervous system who lose bladder control, may need a catheter for life.

People who have diabetes mellitus have a higher risk of a UTI because of changes of the immune system. Any disorder that involves suppression of the immune system sets the stage for urinary infection.

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