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Urinary Tract Infections in Adults
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. Each year, urinary tract infections
(UTI's) account for about 8 million doctor visits. Women are
especially prone to UTI's for reasons that are poorly understood. One
woman in five develops a UTI during her lifetime.
The Urinary Tract
The urinary system consists of the kidneys, ureters, bladder, and
urethra. The key players 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 liquid waste 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.
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
live 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 UTI's
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. Despite these safeguards, though, infections
Who Is at Risk
Scientists are not sure why women have more urinary infections than men.
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, is unconscious, or is 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.
UTI's may occur in infants who are born with abnormalities of the
urinary tract that sometimes need to be corrected with surgery. UTI's
are rarely seen in boys and young men. In women, though, the rate of
UTI's 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
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 UTI's. 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 UTI's in a row are due to E.
coli, slight differences in the bacteria indicate distinct
Research funded by the National Institutes of Health (NIH) suggests
that one factor behind recurrent UTI's may be the ability of bacteria
to attach to cells lining the urinary tract. A recent NIH-funded study
has also shown that women with recurrent UTI's tend to have certain
blood types. Some scientists speculate that women with these blood
types are more prone to UTI's 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 UTI's.
Infections in Pregnancy
Pregnant women seem no more prone to UTI's 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
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 if there is a
change in the child's urinary pattern.
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
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 only be detected
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 are taken. The film shows an outline of the
urinary tract, revealing even small changes in the structure of the
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.
An uncomplicated UTI can be cured with 1 or 2 days of treatment.
UTI's are treated with antibacterial drugs. The choice of drug and
length of treatment depends 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 UTI's
are trimethoprim (Trimpex), trimethoprim/sulfamethoxazole (Bactrim,
Septra, Cotrim), amoxicillin (Amoxil, Trimox, Wymox), nitrofurantoin
(Macrodantin, Furadantin), and ampicillin.
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
Various drugs are available to relieve the pain of a UTI. A heating
pad or a warm bath may also help. Most doctors suggest that drinking
plenty of water helps cleanse the urinary tract of bacteria. For the
time being, 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.)
Recurrent Infections in Women
Women who have frequent recurrences may benefit from preventive
About 4 out of 5 women who have a UTI get another in 18 months. 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
Dipsticks that change color when an infection is present are now
available without 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 UTI's 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:
Infections in Pregnancy
- Drink plenty of water every day. Some doctors suggest drinking
cranberry juice, which in large amounts inhibits the growth of some
bacteria by acidifying the urine. Vitamin C (Ascorbic Acid)
supplements have the same effect;
- 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.
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.
UTI's are unusual in men. They usually stem from an
obstruction--for example, a urinary stone or enlarged prostate--or 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 recommended lengthier therapy in men than in women,
in part to prevent infections of the prostate gland. Prostate
infections (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.
Research in Urinary System Disorders
The NIH conducts and supports a variety
of research in diseases of the kidney and urinary tract. The knowledge
gained from these studies is advancing scientific understanding of why
UTI's develop and is leading to improved methods of diagnosing,
treating, and preventing infections.
The National Institute of Diabetes and Digestive and Kidney
Diseases, part of the NIH, has established six research centers around
the country with the goal of reducing the major causes of kidney and
urinary tract diseases through innovative research. The lead
researchers, their institutions, and research focus are listed on the
George M. O'Brien Kidney and Urological Research Centers
M. Brenner, M.D.
Division of Nephrology
Brigham and Women's
75 Francis Street
Boston, Massachusetts 02115
Kidney Disease of Diabetes Mellitus
Kidney Transplant Rejection
Roger C. Wiggins, M.D.
Division of Nephrology
3914 Taubman Center
1500 East Medical Center
Ann Arbor, Michigan 48109-0364
Harry R. Jacobson, M.D.
53223 Medical Center North
21st Avenue, South
Nashville, Tennessee 37232-2732
Progressive Glomerular Sclerosis
David G. Warnock, M.D.
Division of Nephrology
of Alabama at Birmingham
Room 647 THT, UAB Station
Birmingham, Alabama 35294
High Blood Pressure on the Kidney
Ahmad Elbadawi, M.D.
SUNY Upstate Center
750 East Adams
Syracuse, New York 13210
Urinary Tract Obstruction
John T. Glayhack, M.D.
Department of Urology
303 East Chicago Avenue
Chicago, Illinois 60611
The following materials can be found in
medical libraries, many college and university libraries, and through
interlibrary loan in most public libraries.
Corriere, Joseph N. Jr. et al., "Cystitis: Evolving Standard
of Care," Patient Care, Feb. 29, 1988, pp. 3347.
Fowler, Jackson E. Jr., "Urinary Tract Infections in Women,"
Urologic Clinics of North America, Nov. 1986, pp.
Gillenwater, Jay Y. et al., eds. Adult and Pediatric Urology,
vol. 1. Chicago: Yearbook Medical Publishers, 1987.
Goldman, Peggy L. et al., "Evaluating Dysuria in the Era of
STDs," Patient Care, January 15, 1991, pp. 51-69.
Hooton, Thomas M. et al., "Escherichia coli Bacteriuria and
Contraceptive Method," Journal of the American Medical
Association, January 2, 1991, pp. 64-69.
Krieger, John N., "Complications and Treatment of Urinary
Tract Infections During Pregnancy," Urologic Clinics of
North America, Nov. 1986, pp. 685-693.
Kunin, Calvin M. Detection,Prevention and Management of Urinary
Tract Infections, 4th edition. Philadelphia: Lea and Febiger,
Prostate Enlargement: Benign Prostatic Hyperplasia. A
patient education booklet prepared by the National Institute of
Diabetes and Digestive and Kidney Diseases, NIH, 1991.
Sheinfeld, Joel et al., "Association of the Lewis Blood-Group
Phenotype with Recurrent Urinary Tract Infections in Women," New
England Journal of Medicine, March 23, 1989, pp 773-776.
Spencer, Julia R., and Schaeffer, Anthony J., "Pediatric
Urinary Tract Infections," Urologic Clinics of North America,
Nov. 1986, pp. 661-672.
Stamm, Walter E. et al., "Acute Renal Infection in Women:
Treatment with Trimethoprim-Sulfamethoxazole or Ampicillin for Two or
Six Weeks: A Randomized Trial," Annals of Internal Medicine,
March 1987, pp. 341-345.
Stapleton, Ann et al., "Postcoital Antimicrobial Prophylaxis
for Urinary Tract Infection: a randomized, double-blind,
placebo-controlled trial," Journal of the American Medical
Association, August 8, 1990, pp. 703-706.
Walsh, Patrick C. et al., eds.Campbell's Urology, vol 1.
5th edition. Philadelphia: W.B. Saunders, 1986.
National Kidney and Urologic Diseases Information Clearinghouse
3 Information Way
Bethesda, MD 20892-3580
The National Kidney and Urologic Diseases Information Clearinghouse
(NKUDIC) is a service of the National Institute of Diabetes and
Digestive and Kidney Diseases (NIDDK). The NIDDK is part of the
National Institutes of Health under the U.S. Public Health Service.
Established in 1987, the clearinghouse provides information about
diseases of the kidneys and urologic system to people with kidney and
urologic disorders and to their families, health care professionals,
and the public. NKUDIC answers inquiries; develops, reviews, and
distributes publications; and works closely with professional and
patient organizations and Government agencies to coordinate resources
about kidney and urologic diseases.
Information provided by the NIH.