Urinary Tract Infection
Urinary tract infection (UTI) is a common infection that usually occurs when
bacteria enter the opening of the urethra and multiply in the urinary tract. The
urinary tract includes the kidneys, ureters (tubes that carry urine from the
kidneys to the bladder), bladder, and urethra (tube that carries urine from the
bladder). The special connection of the ureters at the bladder help prevent
urine from backing up into the kidneys, and the flow of urine through the
urethra helps to eliminate bacteria. Men, women, and children develop UTIs.
Urinary tract infections usually develop first in the lower urinary tract
(urethra, bladder) and, if not treated, progress to the upper urinary tract (ureters,
kidneys). Bladder infection (cystitis) is by far the most common UTI.
Infection of the urethra is called urethritis. Kidney infection (pyelonephritis)
requires urgent treatment and can lead to reduced kidney function and possibly
even death in untreated, severe cases.
Incidence and Prevalence
Approximately 8 to 10 million people in the United States develop a UTI each
year. Women develop the condition much more often than men, for reasons that are
not fully known, although the much shorter female urethra is suspected. The
condition is rare in boys and young men.
Twenty percent of women in the United States develop a UTI and 20% of those
have a recurrence. Urinary tract infections in children are more common in those
under the age of 2.
Causes and Risk Factors
Escherichia coli (E. coli) causes about 80% of UTIs in adults. These
bacteria are normally present in the colon and may enter the urethral opening
from the skin around the anus and genitals. Women may be more susceptible to UTI
because their urethral opening is near the source of bacteria (e.g., anus,
vagina) and their urethra is shorter, providing bacteria easier access to the
bladder. Other bacteria that cause urinary tract infections include
Staphylococcus saprophyticus (5 to 15% of cases), Chlamydia trachomatis,
and Mycoplasma hominis. Men and women infected with chlamydia
trachomatis or mycoplasma hominis can transmit the bacteria to their
partner during sexual intercourse, causing UTI.
Sexual intercourse triggers UTI in some women, for unknown reasons. Women who
use a diaphragm develop infections more often, and condoms with spermicidal foam
may cause the growth of E. coli in the vagina, which may enter the
Urinary catheterization (small tube inserted into the bladder through
the urethra to drain urine) can also cause UTI by introducing bacteria into the
urinary tract. The risk for developing a UTI increases when long-term
catheterization is required.
In infants, bacteria from soiled diapers can enter the urethra and cause UTI.
E. coli may also enter the urethral opening when young girls do not wipe from
front to back after a bowel movement.
Other risk factors include the following:
- Bladder outlet obstructions (e.g., kidney stones,
- Conditions that cause incomplete bladder emptying (e.g., spinal cord
- Congenital (present at birth) abnormalities of the urinary tract (e.g.,
- Suppressed immune system
- Being uncircumcised
Certain blood types enable bacteria to attach more easily to cells that line
the urinary tract, causing recurrent UTIs.