After the flu and common cold, urinary tract infections (UTIs) are the most common medical complaint among women in their reproductive years. UTIs are far more common among women than among men. Most women will develop a UTI at some time in their lives, and many will have recurrences.
Specific Risk Factors in Women
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 at the anal opening can be easily transferred to the opening of 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 in premenopausal women occur within 24 hours of intercourse. UTIs are very rare in celibate women. However, UTIs are NOT sexually transmitted infections.
In general, it is the physical act of intercourse itself that produces conditions that increase susceptibility to the UTI bacteria, with some factors increasing the risk. For example, women having sex for the first time or who have intense or frequent sex are at risk for a condition called "honeymoon cystitis."
Certain types of contraceptives can also increase the risk of UTIs. In particular, women who use diaphragms tend to develop UTIs. The spring-rim of the diaphragm can bruise the area near the bladder, making it susceptible to bacteria. Spermicidal foam or gel used with diaphragms, and spermicidal-coated condoms, also increase susceptibility to UTIs. Most spermicides contain nonoxynol-9, a chemical that is associated with increased UTI risk.
Pregnancy. In pregnant women, the presence of asymptomatic bacteriuria is associated with increased risk of kidney infection, which can cause early labor and other serious pregnancy complications. For this reason, pregnant women should be screened and treated for asymptomatic bacteriuria. Pregnant women are more susceptible to kidney infection because as the uterus enlarges it compresses the ureters and bladder. This causes urine to back up into the kidney, increasing the risk of bacterial infection.
Menopause. The risk for UTIs, both symptomatic and asymptomatic, is highest in women after menopause. This is primarily due to decrease in estrogen, which thins the walls of the urinary tract and reduces its ability to resist bacteria. Estrogen loss can also reduce certain immune factors in the vagina that help block E. coli from adhering to vaginal cells. For some women, topical estrogen therapy helps restore healthy bacteria and reduce the risk of recurrent UTIs. (Oral hormone replacement therapy is not helpful for UTIs.)
Other aging-related urinary conditions, such as urinary incontinence, can increase the risk for recurrent urinary tract infections.
Allergies. 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 increased risk for UTIs. In such cases, the allergies may cause small injuries that can introduce bacteria.
Antibiotic Use. Antibiotics often eliminate lactobacilli, the protective bacteria, along with harmful bacteria. This can cause an overgrowth of E. coli in the vagina.
Specific Risk Factors in Men
Men become more susceptible to UTIs after age 50, when they begin to develop prostate problems. Benign prostatic hyperplasia (BPH), enlargement of the prostate gland, can produce obstruction in the urinary tract and increase the risk for infection. In men, recurrent urinary tract infections are also associated with prostatitis, an infection of the prostate gland. Although only about 20% of UTIs occur in men, these infections can cause more serious problems than they do in women. Men with UTIs are far more likely to require hospitalization than women.
Specific Risk Factors in Children
UTIs are rare during infancy but they are much more common in boys than in girls. Boys who are circumcised are far less likely than uncircumcised boys to develop UTIs by the time they are 1 year old. After the age of 2 years, UTIs are more common in girls. As with adults, E. coli is the most common cause of UTIs in children.
Vesicoureteral Reflux (VUR). Vesicoureteral reflux (VUR) is the cause of up to half of urinary tract infections that occur during childhood. VUR also puts children at risk for UTI recurrence.
VUR is a condition in which the urine backs up into the kidneys. Normally, when the bladder becomes filled, the muscle in the wall of the bladder contracts, and the urine leaves the body via another tube called the urethra. There is a valve-like mechanism where the ureters join the bladder. These valves' job is to keep urine from flowing backward towards the kidneys when the bladder contracts. If the valves do not work well, urine may remain in the bladder where bacteria can grow. The back flow of urine may also carry any infection from the bladder up into the kidneys.
Click the icon to see an image of vesicoureteral reflux.
Catheterization and UTI Risk
Most UTIs that develop in hospitalized patients are due to urinary catheters. The longer any urinary catheter is in place, the higher the risk for growth of bacteria and an infection. In most cases of catheter-induced UTIs, there are 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.
All older adults who are immobilized, catheterized, or dehydrated are at increased risk for UTIs. Nursing home residents, particularly those who are incontinent, are at very high risk.
Medical Conditions that Increase the Risk of 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 does not affect this condition.) The risk for UTI complications, and fungal-related UTIs, is also higher in people with diabetes.
Kidney Problems. Nearly any kidney disorder, including kidney stones, increases the risk for complicated UTIs.
Neurogenic Bladder. A number of brain and nerve disorders can affect the nerves of the bladder and cause problems with the ability to empty the bladder and control urine leakage. Multiple sclerosis, stroke, spinal cord injury, and diabetic neuropathy are common examples.
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.
Immune System Problems. People with immunocompromised systems, such as those who have HIV/AIDS or who are undergoing treatment for cancer, are at increased risk for all types of infections, including UTIs and pyelonephritis.
Urinary Tract Abnormalities. Some people have structural abnormalities of the urinary tract that cause urine to stagnate or flow backward into the upper urinary tract. 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.