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Self-infection
Most urinary tract infections are caused by bacteria that have traveled to the urinary tract from the person's own intestine or (in women) vagina.
Other causes of urinary tract infections
Taking antibiotics for another medical problem
Having taken antibiotics recently for any reason may have changed the type and number of bacteria in the vagina and urethra. Those changes can make it easier for infection-causing bacteria to grow in and around the opening of the urethra, increasing the chances that an infection will develop there.
Prostate infection
In men, a bacterial infection of the prostate gland (prostatitis) greatly increases the chances that a urinary tract infection will develop.
Especially for women
Sexual activity and contraception
Many women regularly develop bladder infections within a couple of days after having sexual intercourse.
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Profile of urinary tract (female) |
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| Sexual activity may increase the chances of developing a urinary tract infection if the penis bruises the woman's urethra during intercourse or if the penis or other sexual activity introduces disease-causing bacteria into the woman's urethra. Women in their late teens and early twenties are up to 60 times more likely to develop a urinary tract infection within 48 hours after vaginal intercourse as women of the same age who do not have intercourse.
Using a diaphragm, sperm-killing (spermicidal) jelly, or both increases the chances of developing a urinary tract infection.
Spermicidal jellies, whether used with or without a diaphragm, kill not only sperm but also "good" bacteria in the vagina that protect it against infection. Having fewer protective bacteria in the vagina allows potential disease-causing organisms (pathogens) to take their place. As the number of pathogens increases, so do the chances of developing a urinary tract infection.
Relationship to the menstrual cycle
Most of the length of the urethra in women is lined with the same kind of cells that line the vagina. These cells respond to the female sex hormones, estrogen and progesterone, as the vaginal cells do.
Disease-causing (pathogenic) bacteria such as E. coli attach themselves to the cells that line the urethra before they can start an infection. Estrogen and progesterone cause these cells to slide off the inside edges (walls) of the bladder and urethra, taking with them any bacteria that may be attached to them at the time. The cells and bacteria that have fallen off are then washed out of the urinary tract during urination.
All this may help to explain why some women keep getting urinary tract infections while other women never get them or get them once in a while. During the early part of the menstrual cycle, it is easier for bacteria that cause infection to stick to the cells of the urethra. Soon after ovulation, it is harder for those bacteria to stick to the cells of the urethra. In women who tend to get urinary tract infections again and again, bacteria tend to remain in the urethra longer.
After menopause, women's bodies produce much less estrogen than they did before. Low estrogen levels may be one reason that women are more likely to develop urinary tract infections after reaching menopause. Estrogen deficiency may be responsible for several changes in the body that increase the likelihood of developing urinary tract infections.
Leakage of urine (urinary incontinence), which becomes more common after menopause, may encourage infection-causing bacteria to grow in the bladder and around the place where the urethra carries urine out of the body.
Pregnancy
Changes in the urogenital tract during pregnancy increase the chances that pregnant women will develop urinary tract infections. For example, during pregnancy, the tubes that connect the kidney and bladder (the ureters) become enlarged. In addition, the bladder becomes able to hold more urine than usual without hurting. These changes can start in the early months of pregnancy. Such physical changes are more likely to occur during a woman's first pregnancy or if she has had many pregnancies close together.
The ureters can also become partially blocked as the growing uterus puts pressure on them.
A pregnant woman who has large numbers of bacteria in her urine is at risk of getting a urinary tract infection, especially if she:
is older
engages in sexual activity during pregnancy
has diabetes
has sickle cell trait
has had one or more urinary tract infections before
The increased chances of developing a urinary tract infection during pregnancy is a concern for several reasons. First, having such an infection increases the likelihood of having the baby prematurely. Second, the development of a kidney infection in a pregnant woman can be serious for the health of both the mother and the fetus.
After menopause
The lining of the vagina gets thinner after menopause because the body produces less estrogen after menstruation stops. The vaginal fluid also becomes less acidic and therefore less able to fight off harmful bacteria.
Both of these changes make it easier for disease-causing bacteria and other disease-causing microorganisms (pathogens) to multiply. The loss of natural estrogen can prevent the bladder from emptying completely. This situation increases the chances of getting urinary tract infections.
Physical causes of UTIs
Anatomy
Certain anatomic abnormalities increase a person's chances of developing urinary tract infections.
These rare abnormalities are often discovered at an early age because the child has repeated infections. In very young children, urinary tract infections are especially worrisome because they can lead to kidney infections and scarring of the kidney.
Abnormalities include backflow of urine, unusual connections to the bladder or urethra, and blockages somewhere in the urinary tract or kidney.
Women
Some women have an inborn (genetic) tendency that makes their bodies more likely than other women's bodies to allow E. coli bacteria, which cause urinary tract infections, to stick to bladder cells and infect them.
Women who have a shorter urethra than usual or a shorter distance from the urethral opening to the anus may be more likely to develop urinary tract infections.
Men
An enlarged prostate (benign prostatic hypertrophy) is a common cause of urinary tract blockage, which increases the chances of developing a urinary tract infection. Enlargement of the prostate is common in men over age 50. This condition may cause some discomfort, but it is not a disease and usually does not lead to cancer (the reason it is called "benign").
Failure to empty the bladder completely
People who have trouble emptying their bladders completely when they urinate are more likely than other people to develop urinary tract infections. When some urine remains in the bladder after urination, any bacteria that are in the urine or that have attached themselves to cells that have fallen off the bladder wall remain in the bladder instead of leaving it along with the flow of urine. These bacteria may then cause an infection.
How can this happen?
Mechanical problems can prevent the bladder from emptying completely.
Something literally gets in the way
Something may be partially blocking the flow of urine near the area where the urethra joins the bladder.
There may be a problem related to the valves that regulate the release of urine from the bladder.
The urethra may be partially blocked.
In men, an enlarged prostate gland (common after age 50) can hinder the flow of urine.
Damage to the nerves
Nerve damage can prevent the bladder from emptying completely. Possible causes include diseases, such as poliomyelitis (polio) and diabetes, and a spinal cord injury, such as from an accident.
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