Urinary Tract Infections in Adults
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The urinary tract
Urinary tract infections are a serious health problem
affecting millions of people each year.
Infections of the urinary tract are common--only respiratory
infections occur more often. In 1997, urinary tract infections (UTIs)
accounted for about 8.3 million doctor visits.* Women are
especially prone to UTIs for reasons that are poorly understood.
One woman in five develops a UTI during her lifetime. UTIs in
men are not so common, but they can be very serious when they do
*Ambulatory Care Visits to Physician Offices, Hospital
Outpatient Departments, and Emergency Departments: United
States, 1997. Vital and Health Statistics. Series 13,
No. 143. Atlanta, GA: National Center for Health Statistics,
Centers for Disease Control and Prevention, U.S. Dept. of
Health and Human Services; November 1999.
The urinary system consists of the kidneys, ureters, bladder,
and urethra. The key elements in the system are the kidneys, a
pair of purplish-brown organs located below the ribs toward the
middle of the back. The kidneys remove excess liquid and wastes
from the blood in the form of urine, keep a stable balance of
salts and other substances in the blood, and produce a hormone
that aids the formation of red blood cells. Narrow tubes called
ureters carry urine from the kidneys to the bladder, a
triangle-shaped chamber in the lower abdomen. Urine is stored in
the bladder and emptied through the urethra.
The average adult passes about a quart and a half of urine
each day. The amount of urine varies, depending on the fluids
and foods a person consumes. The volume formed at night is about
half that formed in the daytime.
What are the causes of UTI?
Normal urine is sterile. It contains fluids, salts, and waste
products, but it is free of bacteria, viruses, and fungi. An
infection occurs when microorganisms, usually bacteria from the
digestive tract, cling to the opening of the urethra and begin
to multiply. Most infections arise from one type of bacteria,
Escherichia coli (E. coli), which normally lives in the
In most cases, bacteria first begin growing in the urethra.
An infection limited to the urethra is called urethritis. From
there bacteria often move on to the bladder, causing a bladder
infection (cystitis). If the infection is not treated promptly,
bacteria may then go up the ureters to infect the kidneys
Microorganisms called Chlamydia and Mycoplasma
may also cause UTIs in both men and women, but these infections
tend to remain limited to the urethra and reproductive system.
Unlike E. coli, Chlamydia and Mycoplasma
may be sexually transmitted, and infections require treatment of
The urinary system is structured in a way that helps ward off
infection. The ureters and bladder normally prevent urine from
backing up toward the kidneys, and the flow of urine from the
bladder helps wash bacteria out of the body. In men, the
prostate gland produces secretions that slow bacterial growth.
In both sexes, immune defenses also prevent infection. But
despite these safeguards, infections still occur.
Who is at risk?
Some people are more prone to getting a UTI than others. Any
abnormality of the urinary tract that obstructs the flow of
urine (a kidney stone, for example) sets the stage for an
infection. An enlarged prostate gland also can slow the flow of
urine, thus raising the risk of infection.
A common source of infection is catheters, or tubes, placed
in the bladder. A person who cannot void or who is unconscious
or critically ill often needs a catheter that stays in place for
a long time. Some people, especially the elderly or those with
nervous system disorders who lose bladder control, may need a
catheter for life. Bacteria on the catheter can infect the
bladder, so hospital staff take special care to keep the
catheter sterile and remove it as soon as possible.
People with diabetes have a higher risk of a UTI because of
changes in the immune system. Any disorder that suppresses the
immune system raises the risk of a urinary infection.
UTIs may occur in infants who are born with abnormalities of
the urinary tract, which sometimes need to be corrected with
surgery. UTIs are rarely seen in boys and young men. In women,
though, the rate of UTIs gradually increases with age.
Scientists are not sure why women have more urinary infections
than men. One factor may be that a woman's urethra is short,
allowing bacteria quick access to the bladder. Also, a woman's
urethral opening is near sources of bacteria from the anus and
vagina. For many women, sexual intercourse seems to trigger an
infection, although the reasons for this linkage are unclear.
According to several studies, women who use a diaphragm are
more likely to develop a UTI than women who use other forms of
birth control. Recently, researchers found that women whose
partners use a condom with spermicidal foam also tend to have
growth of E. coli bacteria in the vagina.
Many women suffer from frequent UTIs. Nearly 20 percent of
women who have a UTI will have another, and 30 percent of those
will have yet another. Of the last group, 80 percent will have
Usually, the latest infection stems from a strain or type of
bacteria that is different from the infection before it,
indicating a separate infection. (Even when several UTIs in a
row are due to E. coli, slight differences in the
bacteria indicate distinct infections.)
Research funded by the National Institutes of Health (NIH)
suggests that one factor behind recurrent UTIs may be the
ability of bacteria to attach to cells lining the urinary tract.
A recent NIH-funded study found that bacteria formed a
protective film on the inner lining of the bladder in mice. If a
similar process can be demonstrated in humans, the discovery may
lead to new treatments to prevent recurrent UTIs. Another line
of research has indicated that women who are "non-secretors" of
certain blood group antigens may be more prone to recurrent UTIs
because the cells lining the vagina and urethra may allow
bacteria to attach more easily. Further research will show
whether this association is sound and proves useful in
identifying women at high risk for UTIs.
Infections in Pregnancy
Pregnant women seem no more prone to UTIs than other women.
However, when a UTI does occur, it is more likely to travel to
the kidneys. According to some reports, about 2 to 4 percent of
pregnant women develop a urinary infection. Scientists think
that hormonal changes and shifts in the position of the urinary
tract during pregnancy make it easier for bacteria to travel up
the ureters to the kidneys. For this reason, many doctors
recommend periodic testing of urine.
What are the symptoms of UTI?
Not everyone with a UTI has symptoms, but most people get at
least some. These may include a frequent urge to urinate and a
painful, burning feeling in the area of the bladder or urethra
during urination. It is not unusual to feel bad all over--tired,
shaky, washed out--and to feel pain even when not urinating.
Often women feel an uncomfortable pressure above the pubic bone,
and some men experience a fullness in the rectum. It is common
for a person with a urinary infection to complain that, despite
the urge to urinate, only a small amount of urine is passed. The
urine itself may look milky or cloudy, even reddish if blood is
present. A fever may mean that the infection has reached the
kidneys. Other symptoms of a kidney infection include pain in
the back or side below the ribs, nausea, or vomiting.
In children, symptoms of a urinary infection may be
overlooked or attributed to another disorder. A UTI should be
considered when a child or infant seems irritable, is not eating
normally, has an unexplained fever that does not go away, has
incontinence or loose bowels, or is not thriving. The child
should be seen by a doctor if there are any questions about
these symptoms, especially a change in the child's urinary
How is UTI diagnosed?
To find out whether you have a UTI, your doctor will test a
sample of urine for pus and bacteria. You will be asked to give
a "clean catch" urine sample by washing the genital area and
collecting a "midstream" sample of urine in a sterile container.
(This method of collecting urine helps prevent bacteria around
the genital area from getting into the sample and confusing the
test results.) Usually, the sample is sent to a laboratory,
although some doctors' offices are equipped to do the testing.
In the urinalysis test, the urine is examined for white and
red blood cells and bacteria. Then the bacteria are grown in a
culture and tested against different antibiotics to see which
drug best destroys the bacteria. This last step is called a
Some microbes, like Chlamydia and Mycoplasma,
can be detected only with special bacterial cultures. A doctor
suspects one of these infections when a person has symptoms of a
UTI and pus in the urine, but a standard culture fails to grow
When an infection does not clear up with treatment and is
traced to the same strain of bacteria, the doctor will order a
test that makes images of the urinary tract. One of these tests
is an intravenous pyelogram (IVP), which gives x-ray images of
the bladder, kidneys, and ureters. An opaque dye visible on
x-ray film is injected into a vein, and a series of x rays is
taken. The film shows an outline of the urinary tract, revealing
even small changes in the structure of the tract.
If you have recurrent infections, your doctor also may
recommend an ultrasound exam, which gives pictures from the echo
patterns of soundwaves bounced back from internal organs.
Another useful test is cystoscopy. A cystoscope is an instrument
made of a hollow tube with several lenses and a light source,
which allows the doctor to see inside the bladder from the
How is UTI treated?
UTIs are treated with antibacterial drugs. The choice of drug
and length of treatment depend on the patient's history and the
urine tests that identify the offending bacteria. The
sensitivity test is especially useful in helping the doctor
select the most effective drug. The drugs most often used to
treat routine, uncomplicated UTIs are trimethoprim (Trimpex),
trimethoprim/sulfamethoxazole (Bactrim, Septra, Cotrim),
amoxicillin (Amoxil, Trimox, Wymox), nitrofurantoin
(Macrodantin, Furadantin), and ampicillin. A class of drugs
called quinolones includes four drugs approved in recent years
for treating UTI. These drugs include ofloxacin (Floxin),
norfloxacin (Noroxin), ciprofloxacin (Cipro), and trovafloxin
Often, a UTI can be cured with 1 or 2 days of treatment if
the infection is not complicated by an obstruction or nervous
system disorder. Still, many doctors ask their patients to take
antibiotics for a week or two to ensure that the infection has
been cured. Single-dose treatment is not recommended for some
groups of patients, for example, those who have delayed
treatment or have signs of a kidney infection, patients with
diabetes or structural abnormalities, or men who have prostate
infections. Longer treatment is also needed by patients with
infections caused by Mycoplasma or Chlamydia,
which are usually treated with tetracycline,
trimethoprim/sulfamethoxazole (TMP/SMZ), or doxycycline. A
followup urinalysis helps to confirm that the urinary tract is
infection-free. It is important to take the full course of
treatment because symptoms may disappear before the infection is
Severely ill patients with kidney infections may be
hospitalized until they can take fluids and needed drugs on
their own. Kidney infections generally require several weeks of
antibiotic treatment. Researchers at the University of
Washington found that 2-week therapy with TMP/SMZ was as
effective as 6 weeks of treatment with the same drug in women
with kidney infections that did not involve an obstruction or
nervous system disorder. In such cases, kidney infections rarely
lead to kidney damage or kidney failure unless they go
Various drugs are available to relieve the pain of a UTI. A
heating pad may also help. Most doctors suggest that drinking
plenty of water helps cleanse the urinary tract of bacteria.
During treatment, it is best to avoid coffee, alcohol, and spicy
foods. And one of the best things a smoker can do for his or her
bladder is to quit smoking. Smoking is the major known cause of
Recurrent Infections in Women
Women who have had three UTIs are likely to continue having
them. Four out of five such women get another within 18 months
of the last UTI. Many women have them even more often. A woman
who has frequent recurrences (three or more a year) should ask
her doctor about one of the following treatment options:
- Take low doses of an antibiotic such as TMP/SMZ or
nitrofurantoin daily for 6 months or longer. (If taken at
bedtime, the drug remains in the bladder longer and may be
more effective.) NIH-supported research at the University of
Washington has shown this therapy to be effective without
causing serious side effects.
- Take a single dose of an antibiotic after sexual
- Take a short course (1 or 2 days) of antibiotics when
Dipsticks that change color when an infection is present are
now available without a prescription. The strips detect nitrite,
which is formed when bacteria change nitrate in the urine to
nitrite. The test can detect about 90 percent of UTIs when used
with the first morning urine specimen and may be useful for
women who have recurrent infections.
Doctors suggest some additional steps that a woman can take
on her own to avoid an infection:
- Drink plenty of water every day.
- Urinate when you feel the need; don't resist the urge to
- Wipe from front to back to prevent bacteria around the
anus from entering the vagina or urethra.
- Take showers instead of tub baths.
- Cleanse the genital area before sexual intercourse.
- Avoid using feminine hygiene sprays and scented douches,
which may irritate the urethra.
Some doctors suggest drinking cranberry juice.
Infections in Pregnancy
A pregnant woman who develops a UTI should be treated
promptly to avoid premature delivery of her baby and other risks
such as high blood pressure. Some antibiotics are not safe to
take during pregnancy. In selecting the best treatments, doctors
consider various factors such as the drug's effectiveness, the
stage of pregnancy, the mother's health, and potential effects
on the fetus.
Curing infections that stem from a urinary obstruction or
nervous system disorder depends on finding and correcting the
underlying problem, sometimes with surgery. If the root cause
goes untreated, this group of patients is at risk of kidney
damage. Also, such infections tend to arise from a wider range
of bacteria, and sometimes from more than one type of bacteria
at a time.
Infections in Men
UTIs in men usually stem from an obstruction--for example, a
urinary stone or enlarged prostate--or from a medical procedure
involving a catheter. The first step is to identify the
infecting organism and the drugs to which it is sensitive.
Usually, doctors recommend lengthier therapy in men than in
women, in part to prevent infections of the prostate gland.
Prostate infections (chronic bacterial prostatitis) are
harder to cure because antibiotics are unable to penetrate
infected prostate tissue effectively. For this reason, men with
prostatitis often need long-term treatment with a carefully
selected antibiotic. UTIs in older men are frequently associated
with acute bacterial prostatitis, which can be fatal if not
Is there a vaccine to prevent recurrent UTIs?
In the future, scientists may develop a vaccine that can
prevent UTIs from coming back. Researchers in different studies
have found that children and women who tend to get UTIs
repeatedly are likely to lack proteins called immunoglobulins,
which fight infection. Children and women who do not get UTIs
are more likely to have normal levels of immunoglobulins in
their genital and urinary tracts.
Early tests indicate that a vaccine helps patients build up
their own natural infection-fighting powers. The dead bacteria
in the vaccine do not spread like an infection; instead, they
prompt the body to produce antibodies that can later fight
against live organisms. Researchers are testing injected and
oral vaccines to see which works best. Another method being
considered for women is to apply the vaccine directly as a
suppository in the vagina.