Urinary Tract Infections
The urinary tract is normally free of infectious microscopic organisms (microorganisms). But microorganisms sometimes manage to get into the urinary tract and cause infections. An infection anywhere along the urinary tract is called a urinary tract infection (UTI).
Urine is produced by the two kidneys. Each kidney has a collection area for urine, called the renal pelvis. Each renal pelvis drains into a ureter, which channels the urine to the bladder. The bladder empties into a single tube called the urethra. The urethra channels urine outside of the body. In a man, the opening of the urethra is at the tip of the penis. In a woman, the opening is at the vulva.
See the figure A Look at the Urinary Tract.
UTIs are usually confined to the bladder (cystitis). Much less often, microorganisms move up one of the ureters from the bladder, resulting in an infection of the kidney (pyelonephritis).
UTIs are very common in older people. Women are affected more often than men, although this difference narrows with aging. Most UTIs, at their worst, are annoying and distressing. However, pyelonephritis may be more serious. Occasionally UTIs spread into the bloodstream (sepsis), causing serious problems and even death. Fortunately, most UTIs respond very well to treatment.
Microorganisms that cause UTIs almost always come from the skin at or near the opening of the urethra. Microorganisms that enter the urinary tract through the opening of the urethra are usually washed back out by the flushing action of urine. However, some manage to spread upward, where they can cause a UTI.
Very rarely, microorganisms from an infection elsewhere in the body pass from the blood into the kidneys, causing a kidney infection. Also very rarely, a process such as cancer in the colon or rectum can cause a passageway to form between the intestine and the bladder (vesicoenteric fistula), through which bacteria can travel to cause infection. Microorganisms are then able to move into the urinary tract, resulting in a UTI. In women, an infection in the vagina can cause a passageway to form between the vagina and the bladder (vesicovaginal fistula).
Older women are especially prone to UTIs. Women have a shorter urethra than men, thus microorganisms have a shorter distance to travel to reach the bladder. Also, the drop in estrogen level with menopause leads to thinning and inflammation of the urethra's lining, weakening its defense against infection.
In older men, the prostate gland grows larger (a condition called benign prostatic hyperplasia) and compresses the urethra enough to interfere with urine outflow. Among some older people, urine outflow from the bladder can be abnormal because bladder muscles contract weakly or the nerves to the bladder are damaged (neurogenic bladder). Some older women develop a bulge in the bladder (cystocele) that can interfere with urine outflow. Regardless of the cause, when urine outflow is slowed or reduced, urine stagnates. Microorganisms are especially likely to multiply and cause infection in stagnant urine.
The prostate gland may become infected (prostatitis), and microorganisms can intermittently spread from the prostate into the urinary tract, causing a UTI. Medical procedures that require insertion of devices into the urinary tract may cause UTIs. The most common is insertion of a urinary catheter—a hollow, flexible tube placed in the bladder to drain urine. Use of urinary catheters is most common in hospitals and nursing homes, especially in people who have had surgery or who have medical conditions that interfere with the ability to urinate. Occasionally, an infection develops after insertion of an instrument to examine the inside of the ureters (ureteroscope) or urethra and bladder (cystoscope).
Although almost any kind of microorganism can cause a UTI, bacteria are almost always the culprits. Escherichia coli is the bacteria most often responsible for UTIs. Klebsiella, Enterobacter, Proteus, and Pseudomonas also cause infections. Less often, other bacteria, such as Enterococcus and Staphylococcus, cause UTIs. Fungi (such as Candida) and viruses rarely infect the urinary tract.
Cystitis, an infection in the bladder, often results in a painful burning sensation (dysuria) and in a need to urinate frequently, often at night (nocturia) and urgently. The urgent need to urinate may cause an uncontrollable loss of urine (incontinence).
Fever is uncommon unless the infection has spread to become an upper UTI or spread to the blood (sepsis). Flank pain may result from an infected kidney (pyelonephritis). Confusion can develop, especially if the UTI involves a high fever.
The urine may smell especially foul or appear cloudy or bloody. In the very rare instance of a vesicoenteric and vesicovaginal fistula, air may pass through the urethra with urine (pneumaturia), producing bubbles.
Sometimes bacteria get into the bladder and remain there for varying amounts of time without causing any symptoms (sometimes called asymptomatic bacteriuria). This process is most likely to occur in a person whose bladder is not emptying adequately because of nerve damage and virtually always occurs after several weeks in a person who has a permanently placed catheter.
A doctor suspects cystitis on the basis of the symptoms alone. Tests on a urine sample confirm the diagnosis.
A urine sample is obtained by first cleansing the skin surrounding the urethra with an antiseptic wipe, then urinating into a sterile container. If the person is unable to manage because of limited dexterity or an inability to understand instructions, a health care practitioner may need to assist. Occasionally, the urine in the container contains microorganisms that were not cleansed from the skin by wiping before urination. In these instances, a urine sample can be obtained by inserting a catheter into the bladder.
The urine is examined under a microscope to check for the presence of white blood cells and microorganisms. The urine may also be sent to the laboratory to grow and identify the microorganism (urine culture).
The urine is sometimes tested with strips (dip sticks) to check for the presence of nitrites (substances released by bacteria) and leukocyte esterase (a protein found in white blood cells) whose function is to fight infection. These substances indicate that an infection may be present in the urinary tract.
A complete blood count test is often done to check for a high white blood cell count, a possible sign of infection. Blood can also be tested to grow and identify any microorganisms that may have spread from the urinary tract into the bloodstream.
Additional tests are rarely needed but may be done in people who have frequent UTIs. One such test is a measurement of the amount of urine remaining in the bladder after urination is complete (residual urine). Frequent UTIs may also be evaluated by examining the anatomy of the urinary tract with imaging tests, such as an ultrasound, CT scan, cystoscopy, or ureteroscopy.
Improvement of personal hygiene may help prevent UTIs. Antibiotics are sometimes used to prevent infections.
In people who have had a urinary catheter inserted, the catheter is removed as soon as possible to prevent infection.
UTIs that produce symptoms are treated with antibiotics. If fungi are causing the infection, antifungal drugs are used. If a person has a UTI but does not have any symptoms, treatment is not necessary. Drug therapy for a person who does not have symptoms is costly and can cause unwanted side effects. In addition, such therapy can be harmful, because it may allow the microorganism causing the infection to become resistant to the drug that is being given.
Antibiotics are usually taken by mouth. Common choices include trimethoprim-sulfamethoxazole, amoxicillin, ampicillin, cephalexin, ciprofloxacin, levofloxacin, and nitrofurantoin. Other antibiotics are also effective. For the treatment of pyelonephritis, antibiotics are sometimes given through a tube inserted into a vein (intravenously) until symptoms subside. Antibiotics are often taken for 3 days in women and 7 days in men for the treatment of cystitis; pyelonephritis is treated for 7 to 14 days. People with diabetes, a weakened immune system, or an abnormality blocking the flow of urine may need prolonged antibiotic treatment to eradicate the infection.
In conjunction with antibiotics, other drugs are occasionally taken to speed relief of symptoms. Dicyclomine provides temporary relief from the bladder spasms that cause the sensation of urgent urination. Phenazopyridine reduces the burning pain on urination.
Surgery or other procedures (such as insertion of a cystoscope or ureteroscope that includes special instruments) may be necessary to relieve physical blockages to the flow of urine or to correct structural abnormalities in the urinary tract. Draining urine from a blocked area can help control the infection and prevent kidney damage.
UTIs usually respond well to drug therapy. However, a subsequent UTI may develop if the microorganism was not eliminated from the urinary tract during treatment. A second infection caused by the same microorganism is called a relapse infection. Alternatively, infection by one type of microorganism may be followed quickly by an infection caused by a different microorganism. One possible cause of a relapse or recurrent infection is failure to take antibiotics long enough or in a large enough dosage to eliminate the microorganism from the urinary tract. Recurrent infections can occur when abnormalities persist in the urinary tract.