Overview
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, the tubes that carry urine from the kidneys to the
bladder (ureters), bladder, and the tube that carries urine from
the bladder (urethra). 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.
Types
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 urethra.
Urinary catheterization (i.e., insertion of a small tube 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, BPH)
- Conditions that cause incomplete bladder emptying (e.g.,
spinal cord injury)
- Congenital (present at birth) abnormalities of the
urinary tract (e.g., vasicoureteral reflux)
- Suppressed immune system
- Being uncircumcised
