Urinary Tract Infection
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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
occur.
*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.
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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
colon.
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 (pyelonephritis).
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 both partners.
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.
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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
recurrences.
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.
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.
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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 pattern.
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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 sensitivity
test.
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 any bacteria.
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 urethra.
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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 (Trovan).
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
fully cleared.
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 untreated.
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 bladder
cancer.
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
intercourse.
- Take a short course (1 or 2 days) of antibiotics when symptoms
appear.
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
urinate.
- 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.
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.
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 treated immediately.
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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.
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American Foundation for Urologic
Disease
The Prostatitis Foundation
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Bladder Cancer
