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Urinary tract infection - Risk Factors
An in-depth report on the causes, diagnosis, treatment, and prevention of urinary tract infections.
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.
The female and male urinary tracts are relatively the same except for the length 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:
Click the icon to see an image of a diaphragm.
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. Although pregnancy does not increase the rates of asymptomatic bacteriuria, it does increase the risk that it will progress to a full-blown kidney infection, which can cause early labor and other serious pregnancy complications. (However in early pregnancy, frequent urination -- a common symptom of UTI -- is most likely due to pressure on the bladder.) For this reason, pregnant women should be screened and treated for asymptomatic bacteriuria.
Menopause. The risk for UTIs, both symptomatic and asymptomatic, is highest in women after menopause. This is primarily due to estrogen loss, 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.
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 50 years of age, 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 be hospitalized than women. [For more information, see In-Depth Report #71: Benign prostatic hyperplasia.]
Specific Risk Factors in Children
Each year, about 3% of American children develop urinary tract infections. During the first few months of life, UTIs are more common in boys than in girls. Boys who are uncircumcised are about 10 - 12 times more likely than circumcised boys to develop UTIs by the time they are 1 year old. After the age of 2 years, UTIs are far more common in girls. Throughout childhood, the risk of UTIs is about 2% for boys and 8% for girls. As with adults, E. coli is the most common cause of UTIs in children.
Vesicoureteral Reflux (VUR). Vesicoureteral reflux (VUR) affects about 10% of all children and is the cause of up to 50% of urinary tract infections during childhood. VUR also puts children at risk for UTI recurrence.
Normally, when the bladder becomes filled, the muscles in the wall of the bladder squeeze, and the urine leaves the body via another tube called the urethra. There is a valve-like mechanism where the ureter joins the bladder. This valveā ' s job is to keep urine from flowing backward towards the kidneys when the bladder squeezes. If the valve does 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.
Institutionalization, Catheterization, and UTI Risk
Hospitalizations. About 40% of all infections that develop in patients while in the hospital are in the urinary tract. The organisms that cause infections in hospitals (called nosocomial infections) are often 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.
Catheters. About 80% of UTIs in the hospital are due to 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.
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, are at very high risk. Symptoms of urinary tract infection in patients and nursing home residents are often subtle.
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 has no effect on 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.
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