Urinary Tract Infection - Risk Factors

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% to 11% of pregnant women have asymptomatic bacteriuria and, of those, 13% to 27% will develop a kidney infection late in their term. (It should be noted, however, that in early pregnancy, frequent urination, a common symptom of UTI, is most likely due to pressure on the bladder.)

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Although all pregnant women should be tested for UTIs, those at particularly high risk are those with the following conditions or situations:

Diabetes.
Sickle cell trait.
Members of low-income groups.
Women who have had many children.
A history of childhood UTIs.
Women who have undergone a cesarean section with catheterization of the bladder.
Women who 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% to 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. In fact, studies indicate that between 20% and 25% of women over 65 years old have UTIs, and 10% to 15% have asymptomatic bacteriuria (compared to 2% to 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.