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Urinary tract infection

Description

An in-depth report on the causes, diagnosis, treatment, and prevention of urinary tract infections.

Alternative Names

Cystitis; UTI

Risk Factors

After the flu and common cold, urinary tract infections (UTIs) are the most common medical complaint among women in their reproductive years. Women are 30 times more likely to have UTIs than men. Every year, 11% of American women have at least one such infection, and up to 60% of all women will develop a UTI at some time in their lives. A third of these women will have a recurrence within a year. Furthermore, each year about 250,000 women develop kidney infections (pyelonephritis) and 100,000 are hospitalized for treatment.

Structure of the Female Urinary Tract. In general, the higher risk in women is mostly due to the shortness of the female urethra, which is 1.5 inches compared to 8 inches in men. Bacteria from fecal matter can be easily transferred to the vagina or the urethra.

Sexual Behavior. Frequent or recent sexual activity is the most important risk factor for urinary tract infection in young women. Nearly 80% of all urinary tract infections occur within 24 hours of intercourse. (Sexual activity is less associated with cystitis in women after menopause.)

UTIs are very rare in celibate women. It is important to stress, however, that UTIs are not sexually transmitted infections, although these infections ( Chlamydia trachomatis , gonorrhea, or herpes simplex virus) may increase the risk for UTIs.

In general, however, it is the physical act of intercourse itself that produces conditions that increase susceptibility to the UTI bacteria, with some factors increasing the risk:

• Women having sex for the first time or who have intense and frequent sex after a period of abstinence are at risk for a condition called "honeymoon cystitis."
• A sudden increase in the frequency of sexual intercourse poses a significant risk for UTI, particularly if a diaphragm is used.
• Sexual position (such as the woman on top) can contribute to the risk.

Contraceptives may also contribute to risk in a number of ways:

• The spring-rim of the diaphragm may bruise the area near the bladder neck, making it susceptible to bacteria.
• Unlubricated condoms may injure vaginal tissue and make it vulnerable to infections. (Using a sterile water-based lubricant, such as KY jelly, may help reduce this risk. Petroleum-based lubricants should be avoided because they weaken latex condoms.)
• Some women experience UTI as an allergic reaction to latex in condoms or to oral contraceptives.
• Use of spermicide, such as nonoxynol-9, doubles or triples a women's risk for UTI, regardless of whether it is used with a condom or diaphragm. Spermicides also pose a risk for sexually transmitted infections and experts warn against their use.

Pregnancy. Although pregnancy does not increase the rates of asymptomatic bacteriuria, it does increase the risk that it will progress to a full-blown infection. About 2 - 11% of pregnant women have asymptomatic bacteriuria and, of those, 13 - 27% will develop a kidney infection late in their term. (However in early pregnancy, frequent urination -- a common symptom of UTI -- is most likely due to pressure on the bladder.)

Although all pregnant women should be tested for UTIs, women at highest risk have the following conditions or situations:

• Diabetes
• Sickle cell trait
• Low-income
• Have had many children
• History of childhood UTIs
• Have undergone a cesarean section with catheterization of the bladder
• Have received epidural anesthesia

Women who have had a UTI before or during pregnancy also have a higher risk of developing recurrent urinary tract infections after delivery. Approximately 25 - 33% of women who experience bacteriuria during pregnancy will have another urinary tract infection, sometimes as long as 10 to 14 years later.

Menopause. The risk for UTIs, both symptomatic and asymptomatic, is highest in women after menopause. Studies indicate that between 20 - 25% of women over 65 years old have UTIs, and 10 - 15% have asymptomatic bacteriuria (compared to 2 - 5% of young women). Sexual activity plays a lesser role in UTIs in older women than in younger women. In general, biologic changes due to menopause put older women at particular risk for primary and recurring UTIs:

• With estrogen loss, the walls of the urinary tract thin out, weakening the mucous membrane and reducing its ability to resist bacteria. The bladder may lose elasticity and fail to empty completely.
• Estrogen loss has also been associated with reduction in certain immune factors in the vagina that help block E. coli from adhering to vaginal cells.
• Levels of lactobacilli (protective bacteria) decline after menopause, perhaps also due to drops in estrogen.

Some women carry the blood group P1, which as they get older, is associated with high levels of specific cells in the vagina and urethra that bind to a specific strain of E. coli that is resistant to normal infection-fighting mechanisms.

Other Risk Factors in Women. Women who have skin allergies to ingredients in soaps, vaginal creams, bubble baths, or other chemicals that are used in the genital area are at high risk for UTIs. In such cases, the allergies may cause small injuries that can introduce bacteria.

Risk Factors of Recurring Infection in Women

Most women who have had one UTI have occasional recurrences. About 25 - 50% of these women can expect another infection within a year of the previous one.

Between 3 - 5% of women, however, have ongoing, recurrent urinary tract infections, which follow the resolution of a previous treated or untreated episode. The major groups of women who are at highest risk for recurrent infections are young highly sexually active women and postmenopausal women. It might be argued that nearly all women who have a urinary tract infection are at risk for another, particularly if they are not treated for the first one.

Lifestyle Factors Increasing the Risk for Recurrence. Why urinary tract infections become chronic and recurring in many women is not entirely clear, but researchers are identifying certain lifestyle factors that may increase the risk in specific women:

• Engaging in sexual intercourse more than four times a month
• Recent changes in sexual partners
• Having a mother with a history of UTIs
• Having a first UTI before age 15
• Use of spermicides
• Smoking and taking tub baths may also increase the risk for recurrent urinary tract infections, but they are less significant than other risk factors.

Biologic and Physical Factors. Some women may also have certain biologic or anatomical factors that increase the risk for recurring UTIs:

• Having a shorter than average distance between the urethra and the anus.
• Certain women may carry a compound called sialosyl galactosyl globoside (SGG) on the surface of kidney cells, which is a highly powerful receptor for E. coli bacteria.
• Certain women have a genetic susceptibility to becoming infected in the vaginal area with greater numbers of disease-causing organisms that adhere to the lining.
• Certain women may be deficient in human beta-defensin-1 (HBD-1), believed to be a naturally occurring antibiotic.

Risk Factors for Recurrence in the Aging Woman. In addition to menopause, other very strong risk factors for recurrences in older women include urinary incontinence and previous operations on the genital or urinary tracts. Additional risk factors for UTIs in older women include diabetes, vaginal itching or dryness, having had children, and poor overall health.

Risk Factors in Children

About 2% of children develop urinary tract infections. Because males are more likely to be born with structural abnormalities of the urinary tract, UTIs during the first 6 months of life are more common in boys. The rates are about equal in toddlers. Afterward, however, UTIs are far more common in girls. By the age of 5 years, UTIs are 50 times more common in girls than in boys. Within the first 10 years, boys will have a 1% and girls a 3% chance for developing a UTI. An infection reoccurs in about 30% of boys and 40% of girls. As with adults, Eschericia coli ( E. coli ) is the most common cause of UTIs in children.

Vesicoureteral Reflux (VUR). Vesicoureteral reflux (VUR) is the source of urinary tract infections in 30 - 50% of childhood cases. This is a structural defect of the valve-like mechanism between the ureter and bladder that allows urine to flow backward, carrying infection from the bladder up into the kidneys. VUR also puts children at risk for recurrence; such recurrences nearly always occur within the first 6 months after the first UTI.

Risk Factors in Men

Men become more susceptible to UTIs after 50 years of age, when they begin to develop prostate problems. From 5 - 15% of men over 65 will have asymptomatic bacteriuria. Benign prostatic hyperplasia can produce obstruction in the urinary tract and increase the risk for infection. In men, recurrent urinary tract infections are associated with prostatitis, an infection of the prostate gland that can also be caused by E. coli . [For more information, see In-Depth Report #71: Benign prostatic hyperplasia.]

Institutionalization

Hospitalizations and Catheters. About 40% of all infections that develop in hospitalized patients are in the urinary tract. The organisms that cause infections in hospitals (called nosocomial infections) are usually different from those that commonly cause UTIs. They are also more likely to be resistant to standard antibiotics. Hospitalized patients at highest risk for such infections are those with in-dwelling urinary catheters, patients undergoing urinary procedures, long-stay elderly men, and patients with severe medical conditions.

About 80% of UTIs in the hospital are due to catheters. Nearly all patients who need urinary catheters develop high levels of bacteria in their urine, and the longer the catheter is in place, the higher the risk for infection. Catheterized patients who develop diarrhea are nine times more likely to develop UTIs than are patients without diarrhea. In most cases of catheter-induced UTIs, the infection produces no symptoms. Because of the risk for wider infection, however, anyone requiring a catheter should be screened for infection. Catheters should be used only when necessary and should be removed as soon as possible.

Nursing Homes. All older adults who are immobilized, catheterized, or dehydrated are at increased risk for UTIs. Nursing home residents, particularly those who are incontinent and demented, are at very high risk. Up to 40% of elderly patients who live in nursing homes will contract a urinary tract infection.

Anatomical Abnormalities in Adults

Some people have structural abnormalities of the urinary tract that cause urine to stagnate or flow backward into the upper urinary tract. Such conditions include:

• A prolapsed bladder (cystocele) can result in incomplete urination so that urine collects, creating a breeding ground for bacteria.
• Tiny pockets called diverticula sometimes develop inside the urethral wall and can collect urine and debris, further increasing the risk for infection.

Antibiotics as Risk Factors for UTIs

Antibiotics often eliminate lactobacilli , the protective bacteria, along with harmful bacteria. This causes an overgrowth of E. coli in the vagina. In one study, the risk for UTI increased during the 15 to 28 days that women were taking antibiotics. In fact, some research suggests that taking antibiotics for a urinary tract infection increases the risk for a subsequent infection.

Medical Conditions That Increase the Risk for UTIs

Diabetes. Diabetes puts women at significantly higher risk for asymptomatic bacteriuria. The longer a woman has diabetes, the higher the risk. (Control of blood sugar has no effect on this condition.) The risk for UTI complications is also higher in people with diabetes. In fact, certain UTI-related abscesses are reported only in patients with diabetes. These patients are also at higher risk for fungal-related UTIs.

Kidney Problems. Nearly any kidney disorder increases the risk for complicated UTIs.

AIDS and Immunosuppressed Patients. Any infection is dangerous in people whose immune systems are damaged, and UTIs are no exception, particularly pyelonephritis.

Sickle-Cell Anemia. Patients with sickle-cell anemia are particularly susceptible to kidney damage from their disease, and UTIs put them at even greater risk.

Kidney Stones. In some cases, kidney stones can cause urinary tract obstruction that leads to infection, particularly pyelonephritis. Symptoms of severe urinary tract infection in people with a history of kidney stones may indicate obstruction, which is a serious condition.

• Review Date: 6/16/2006
• Reviewed By: Harvey Simon, M.D., Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital

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