Urinary Tract 

Infections in Adults 

National Kidney and Urologic Diseases Information Clearinghouse 

U.S. Department 

of Health and 

Human Services 

NATIONAL 

INSTITUTES 

OF HEALTH 

What is a urinary tract 

infection (UTI)? 

A UTI is an infection in the urinary 

tract. Infections are caused by 

microbes—organisms too small to be seen 

without a microscope—including fungi, 

viruses, and bacteria. Bacteria are the most 

common cause of UTIs. Normally, bacteria that enter the urinary tract are rapidly 

removed by the body before they cause 

symptoms. However, sometimes bacteria 

overcome the body’s natural defenses and 

cause infection. An infection in the urethra 

is called urethritis. A bladder infection is 

called cystitis. Bacteria may travel up the 

ureters to multiply and infect the kidneys. 

A kidney infection is called pyelonephritis. 

What is the urinary tract? 

The urinary tract is the body’s drainage 

system for removing wastes and extra water. 

The urinary tract includes two kidneys, two 

ureters, a bladder, and a urethra. The kidneys are a pair of bean-shaped organs, each 

about the size of a fist and located below the 

ribs, one on each side of the spine, toward 

the middle of the back. Every minute, a person’s kidneys filter about 3 ounces of blood, 

removing wastes and extra water. The wastes 

and extra water make up the 1 to 2 quarts of 

urine a person produces each day. The urine 

travels from the kidneys down two narrow 

Kidney 

Ureter 

Urethra 

Bladder 

The urinary tract 

tubes called the ureters. The urine is then 

stored in a balloonlike organ called the bladder and emptied through the urethra, a tube 

at the bottom of the bladder. 

When the bladder empties, a muscle called 

the sphincter relaxes and urine flows out of 

the body through the urethra. The opening 

of the urethra is at the end of the penis in 

males and in front of the vagina in females. 
 

 

What causes UTIs? 

Most UTIs are caused by bacteria that live 

in the bowel. The bacterium Escherichia coli 

(E. coli) causes the vast majority of UTIs. 

Microbes called Chlamydia and Mycoplasma 

can infect the urethra and reproductive 

system but not the bladder. Chlamydia 

and Mycoplasma infections may be sexually 

transmitted and require treatment of sexual 

partners. 

The urinary tract has several systems to prevent infection. The points where the ureters 

attach to the bladder act like one-way valves 

to prevent urine from backing up toward the 

kidneys, and urination washes microbes 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. Certain bacteria have 

a strong ability to attach themselves to the 

lining of the urinary tract. 

How common are UTIs in 

adults? 

Urinary tract infections are the second 

most common type of infection in the body, 

accounting for about 8.1 million visits to 

health care providers each year.1 Women are 

especially prone to UTIs for anatomical reasons. One factor is that a woman’s urethra is 

shorter, allowing bacteria quicker access to 

the bladder. Also, a woman’s urethral opening is near sources of bacteria from the anus 

and vagina. For women, the lifetime risk 

of having a UTI is greater than 50 percent.2 

UTIs in men are not as common as in women 

but can be serious when they occur. 

Who is at risk for a UTI? 

Although everyone has some risk, some 

people are more prone to getting UTIs than 

others. People with spinal cord injuries or 

other nerve damage around the bladder have 

difficulty emptying their bladder completely, 

allowing bacteria to grow in the urine that 

stays in the bladder. Anyone with an abnormality of the urinary tract that obstructs the 

flow of urine—a kidney stone or enlarged 

prostate, for example—is at risk for a UTI. 

People with diabetes or problems with the 

body’s natural defense system are more likely 

to get UTIs. 

1Schappert SM, Rechtsteiner EA. Ambulatory medical 

care utilization estimates for 2006. National health 

statistics reports; no 8. Hyattsville, MD: National 

Center for Health Statistics; 2008. 

2Griebling TL. Urinary tract infection in women. 

In: Litwin MS, Saigal CS, eds. Urologic Diseases in 

America. Department of Health and Human Services, 

Public Health Service, National Institutes of Health, 

National Institute of Diabetes and Digestive and 

Kidney Diseases. Washington, D.C.: GPO; 2007. 

NIH publication 07–5512:587–619. 

2 Urinary Tract Infections in Adults 
 

 

 

 

Sexual activity can move microbes from 

the bowel or vaginal cavity to the urethral 

opening. If these microbes have special 

characteristics that allow them to live in 

the urinary tract, it is harder for the body 

to remove them quickly enough to prevent 

infection. Following sexual intercourse, 

most women have a significant number of 

bacteria in their urine, but the body normally 

clears them within 24 hours. However, some 

forms of birth control increase the risk of 

UTI. In some women, certain spermicides 

may irritate the skin, increasing the risk of 

bacteria invading surrounding tissues. Using 

a diaphragm may slow urinary flow and allow 

bacteria to multiply. Condom use is also 

associated with increased risk of UTIs, possibly because of the increased trauma that 

occurs to the vagina during sexual activity. 

Using spermicides with diaphragms and condoms can increase risk even further. 

Another common source of infection is 

catheters, or tubes, placed in the urethra 

and bladder. Catheters interfere with the 

body’s ability to clear microbes from the 

urinary tract. Bacteria travel through or 

around the catheter and establish a place 

where they can thrive within the bladder. A 

person who cannot urinate in the normal way 

or who is unconscious or critically ill often 

needs a catheter for more than a few days. 

The Infectious Diseases Society of America 

recommends using catheters for the shortest 

time possible to reduce the risk of a UTI.3 

Recurrent Infections 

Many women suffer from frequent UTIs. 

About 20 percent of young women with a 

first UTI will have a recurrent infection.4 

With each UTI, the risk that a woman will 

continue having recurrent UTIs increases.5 

Some women have three or more UTIs a 

year. However, very few women will have 

frequent infections throughout their lives. 

More typically, a woman will have a period 

of 1 or 2 years with frequent infections, after 

which recurring infections cease. 

Men are less likely than women to have a 

first UTI. But once a man has a UTI, he is 

likely to have another because bacteria can 

hide deep inside prostate tissue. Anyone 

who has diabetes or a problem that makes it 

hard to urinate may have repeat 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 

3Hooton TM, et al. Diagnosis, prevention, and 

treatment of catheter-associated urinary tract infection 

in adults: 2009 international clinical practice guidelines 

from the Infectious Diseases Society of America. 

Clinical Infectious Diseases. 2010;50(5):625–663. 

4Tolkoff-Rubin NE, Cotran RS, Rubin RH. Urinary 

tract infection, pyelonephritis, and reflux nephropathy. 

In: Brenner BM, ed. Brenner & Rector’s The Kidney. 

8th ed. Vol. 2. Philadelphia: Saunders; 2008: 

1203–1238. 

5Schaeffer AJ. Infections of the urinary tract. In: 

Walsh PC, Retik AB, Vaughan ED, Wein AJ, eds. 

Campbell’s Urology. 8th ed. Vol. 1. Philadelphia: 

Saunders; 2002: 515–602. 

3 Urinary Tract Infections in Adults 
 

 

tract. One NIH-funded study found that 

bacteria formed a protective film on the 

inner lining of the bladder in mice.6 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 “nonsecretors” 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. A nonsecretor is a person with an A, 

B, or AB blood type who does not secrete 

the normal antigens for that blood type in 

bodily fluids, such as fluids that line the bladder wall.7 

Infections during Pregnancy 

Pregnant women seem no more prone to 

UTIs than other women. However, when 

a UTI does occur in a pregnant woman, 

it is more likely to travel to the kidneys. 

According to some reports, about 4 to 

5 percent of pregnant women develop 

a UTI.8 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 and cause infection. For this reason, 

6Anderson GG, Palermo JJ, Schilling JD, et al. 

Intracellular bacterial biofilm-like pods in urinary tract 

infections. Science. 2003;301:105–107. 

7Stapleton AE, Nudelman E, Clausen H, Hakomori 

S, Stamm WE. Binding of uropathogenic Escherichia 

coli R45 to glycolipids extracted from vaginal epithelial 

cells is dependent on histo-blood group secretor status. 

Journal of Clinical Investigation. 1992;90;965–972. 

8Sharma JB, Aggarwal S, Singhal S, Kumar S, Roy 

KK. Prevalence of urinary incontinence and other 

urological problems during pregnancy: a questionnaire 

based study. Archives of Gynecology and Obstetrics. 

2009;279(6):845–851. 

4 Urinary Tract Infections in Adults 

health care providers routinely screen pregnant women for bacteria in the urine during 

the first 3 months of pregnancy. 

Are UTIs serious? 

Most UTIs are not serious, but some infections can lead to serious problems, such 

as kidney infections. Chronic kidney 

infections—infections that recur or last a 

long time—can cause permanent damage, 

including kidney scars, poor kidney function, 

high blood pressure, and other problems. 

Some acute kidney infections—infections 

that develop suddenly—can be life threatening, especially if the bacteria enter the bloodstream, a condition called septicemia. 

What are the signs and 

symptoms of a UTI? 

Symptoms of a UTI vary by age, gender, and 

whether a catheter is present. Among young 

women, UTI symptoms typically include a 

frequent and intense urge to urinate and a 

painful, burning feeling in the bladder or 

urethra during urination. The amount of 

urine may be very small. Older women and 

men are more likely to be tired, shaky, and 
 

weak and have muscle aches and abdominal pain. Urine may look cloudy, dark, or 

bloody or have a foul smell. In a person 

with a catheter, the only symptom may be 

fever that cannot be attributed to any other 

cause. Normally, UTIs do not cause fever if 

they are in the bladder. A fever may mean 

the infection has reached the kidneys or has 

penetrated the prostate. Other symptoms of 

a kidney infection include pain in the back or 

side below the ribs, nausea, and vomiting. 

How are UTIs diagnosed? 

To find out whether a person has a UTI, the 

health care provider will ask about urinary 

symptoms and then test a sample of urine 

for the presence of bacteria and white blood 

cells, which are produced by the body to fight 

infection. Because bacteria can be found 

in the urine of healthy individuals, a UTI is 

diagnosed based both on symptoms and a 

laboratory test. The person 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 health care providers’ 

offices are equipped to do the testing. For 

people with recurring infections and patients 

in the hospital, the urine may be cultured. 

The culture is performed by placing part of 

the urine sample in a tube or dish with a substance that encourages any bacteria present 

to grow. Once the bacteria have multiplied, 

which usually takes 1 to 3 days, they can be 

identified. The health care provider may 

also order a sensitivity test, which tests the 

bacteria for sensitivity to different antibiotics 

to see which medication is best for treating 

the infection. 

If a person has recurrent UTIs, the health 

care provider may order some additional 

tests to determine if the person’s urinary 

tract is normal. 

Kidney and bladder ultrasound. Ultrasound 

uses a device, called a transducer, that 

bounces safe, painless sound waves off 

organs to create an image of their structure. 

The procedure is performed in a health 

care provider’s office, outpatient center, or 

hospital by a specially trained technician, and 

the images are interpreted by a radiologist— 

a doctor who specializes in medical imaging; anesthesia is not needed. The images 

can show abnormalities in the kidneys and 

bladder. However, this test cannot reveal all 

important urinary abnormalities or measure 

how well the kidneys work. 

5 Urinary Tract Infections in Adults 
 

Voiding cystourethrogram. This test is an 

x-ray image of the bladder and urethra taken 

while the bladder is full and during urination, 

also called voiding. As the person lies on the 

x-ray table, a health care provider inserts the 

tip of a thin, flexible tube called a catheter 

through the urethra into the bladder. The 

bladder and urethra are filled with a special dye called contrast medium, to make 

the structures clearly visible on the x-ray 

images. The x rays are taken from various 

angles while the bladder is full of contrast 

medium. The catheter is then removed and 

x-ray images are taken during urination. The 

procedure is performed in a health care provider’s office, outpatient center, or hospital 

by an x-ray technician. The technician is 

supervised by a radiologist while the images 

are taken. The radiologist then interprets 

the images. Anesthesia is not needed, but 

light sedation may be used for some people. 

This test can show abnormalities of the 

inside of the urethra and bladder. The test 

can also determine whether the flow of urine 

is normal when the bladder empties. 

Computerized tomography (CT) scan. CT 

scans use a combination of x rays and computer technology to create three-dimensional 

(3-D) images. A CT scan may include the 

injection of contrast medium. CT scans 

require the person to lie on a table that slides 

into a tunnel-shaped device where the x rays 

are taken. The procedure is performed in 

an outpatient center or hospital by an x-ray 

technician, and the images are interpreted 

by a radiologist; anesthesia is not needed. 

CT scans can provide clearer, more detailed 

images to help the health care provider 

understand the problem. 

Magnetic resonance imaging (MRI). MRI 

machines use radio waves and magnets 

to produce detailed pictures of the body’s 

internal organs and soft tissues without using 

x rays. An MRI may include an injection of 

contrast medium. With most MRI machines, 

the person lies on a table that slides into 

a tunnel-shaped device that may be open 

ended or closed at one end; some newer 

machines are designed to allow the person to 

lie in a more open space. The procedure is 

performed in an outpatient center or hospital by a specially trained technician, and 

the images are interpreted by a radiologist; 

anesthesia is not needed though light sedation may be used for people with a fear of 

confined spaces. Like CT scans, MRIs can 

provide clearer, more detailed images. 

6 Urinary Tract Infections in Adults 
 

Radionuclide scan. A radionuclide scan 

is an imaging technique that relies on the 

detection of small amounts of radiation after 

injection of radioactive chemicals. Because 

the dose of the radioactive chemicals is small, 

the risk of causing damage to cells is low. 

Special cameras and computers are used to 

create images of the radioactive chemicals as 

they pass through the kidneys. Radionuclide 

scans are performed in a health care provider’s office, outpatient center, or hospital by a 

specially trained technician, and the images 

are interpreted by a radiologist; anesthesia is 

not needed. Radioactive chemicals injected 

into the blood can provide information about 

kidney function. Radioactive chemicals can 

also be put into the fluids used to fill the 

bladder and urethra for x ray, MRI, and CT 

imaging. 

Urodynamics. Urodynamic testing is any 

procedure that looks at how well the bladder, sphincters, and urethra are storing and 

releasing urine. Most of these tests are 

performed in the office of a urologist—a 

doctor who specializes in urinary problems— 

by a urologist, physician assistant, or nurse 

practitioner. Some procedures may require 

light sedation to keep a person calm. Most 

urodynamic tests focus on the bladder’s 

ability to hold urine and empty steadily and 

completely. Urodynamic tests can also show 

whether the bladder is having abnormal 

contractions that cause leakage. A health 

care provider may order these tests if there 

is evidence that the person has some kind of 

nerve damage. 

Cystoscopy. Cystoscopy is a procedure that 

uses a tubelike instrument to look inside the 

urethra and bladder. Cystoscopy is performed by a doctor in a health care provider’s office, outpatient facility, or hospital with 

local anesthesia. However, in some cases, 

sedation and regional or general anesthesia are needed. Cystoscopy may be used to 

look for swelling, redness, and other signs of 

infection. 

7 Urinary Tract Infections in Adults 
 

How are UTIs treated? 

Most UTIs are caused by bacteria, which are 

treated with bacteria-fighting medications 

called antibiotics or antimicrobials. The 

choice of medication and length of treatment depend on the patient’s history and the 

type of bacteria causing the infection. Some 

antibiotics may be ruled out if a person has 

allergies to them. The sensitivity test takes 

48 hours to complete and is especially useful 

in helping the health care provider select 

the antibiotic most likely to be effective in 

treating an infection. Longer treatment may 

be needed if the first antibiotic given is not 

effective. 

When a UTI occurs in a healthy person with 

a normal, unobstructed urinary tract, the 

term uncomplicated is used to describe the 

infection. Most young women who have 

UTIs have uncomplicated UTIs, which 

can be cured with 2 or 3 days of treatment. 

Single-dose treatment is less effective. 

Longer treatment causes more side effects 

and is not more effective. A follow-up 

urinalysis helps to confirm the urinary tract 

is infection-free. Taking the full course of 

treatment is important because symptoms 

may disappear before the infection is fully 

cleared. 

Complicated UTIs occur when a person—for 

example, a pregnant woman or a transplant 

patient—is weakened by another condition. 

A UTI is also complicated when the person 

has a structural or functional abnormality 

of the urinary tract, such as an obstructive 

kidney stone or prostate enlargement that 

squeezes the urethra. Health care providers should assume that men and boys have a 

complicated UTI until proven otherwise. 

Severely ill patients with kidney infections 

may be hospitalized until they can take 

fluids and needed medications on their own. 

Kidney infections may require several weeks 

of antibiotic treatment. Kidney infections 

in adults rarely lead to kidney damage or 

kidney failure unless they go untreated or are 

associated with urinary tract obstruction. 

Bladder infections are generally self-limiting, 

but antibiotic treatment significantly shortens 

the duration of symptoms. People usually 

feel better within a day or two of treatment. 

Symptoms of kidney and prostate infections last longer. Drinking lots of fluids and 

urinating frequently will speed healing. If 

needed, various medications are available to 

relieve the pain of a UTI. A heating pad on 

the back or abdomen may also help. 

8 Urinary Tract Infections in Adults 
 

Recurrent Infections in Women 

Health care providers may advise women 

who have recurrent UTIs to try one of the 

following treatment options: 

• Take low doses of the prescribed antibiotic daily for 6 months or longer. 

If taken at bedtime, the medication 

remains in the bladder longer and may 

be more effective. NIH-supported 

research 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—2 or 3 days—of an 

antibiotic when symptoms appear. 

To try to prevent an infection, health care 

providers may suggest women 

• drink plenty of water every day 

• urinate when the need arises and avoid 

resisting the urge to urinate 

• urinate after sexual intercourse 

• switch to a different method of birth 

control if recurring UTIs are a problem 

Infections during Pregnancy 

During pregnancy, bacterial infection of the 

urine—even in the absence of symptoms— 

can pose risks to both the mother and the 

baby. Some antibiotics are not safe to take 

during pregnancy. In selecting the best treatments, health care providers consider various 

factors such as the medication’s effectiveness, the stage of pregnancy, the mother’s 

health, and potential effects on the fetus. 

Complicated Infections 

Curing infections that stem from a urinary 

obstruction or other systemic 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 for 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 

Urinary tract infections in men are often the 

result of an obstruction—for example, a urinary stone or enlarged prostate—or are from 

a catheter used during a medical procedure. 

The first step in treating such an infection 

is to identify the infecting organism and the 

medications to which it is sensitive. 

Prostate infections—chronic bacterial 

prostatitis—are harder to cure because antibiotics may be unable to penetrate infected 

prostate tissue effectively. For this reason, 

men with bacterial prostatitis often need 

long-term treatment with a carefully selected 

antibiotic. UTIs in men are frequently 

associated with acute bacterial prostatitis, 

which can be life threatening if not treated 

urgently. 

9 Urinary Tract Infections in Adults 
 

How can recurrent UTIs be 

prevented? 

Changing some daily habits may help a person prevent recurrent UTIs. 

Eating, Diet, and Nutrition 

Drinking lots of fluid can help flush bacteria 

from the system. Water is best. Most people 

should try for six to eight, 8-ounce glasses a 

day. A person who has kidney failure should 

not drink this much fluid. A health care provider should be consulted to learn how much 

fluid is healthy. 

Urination Habits 

A person should urinate often and when the 

urge arises. Bacteria can grow when urine 

stays in the bladder too long. Women and 

men should urinate shortly after sex to flush 

away bacteria that might have entered the 

urethra during sex. Drinking a glass of water 

will also help flush bacteria away. 

After using the toilet, women should wipe 

from front to back. This step is most important after a bowel movement to keep bacteria 

from getting into the urethra. 

Clothing 

Cotton underwear and loose-fitting clothes 

should be worn, so air can keep the area 

around the urethra dry. Tight-fitting jeans 

and nylon underwear should be avoided 

because they can trap moisture and help 

bacteria grow. 

Birth Control 

For women, using a diaphragm or spermicide 

for birth control can lead to UTIs by increasing bacteria growth. A woman who has trouble with UTIs should try switching to a new 

form of birth control. Unlubricated condoms 

or spermicidal condoms increase irritation, 

which may help bacteria grow. Switching to 

lubricated condoms without spermicide or 

using a nonspermicidal lubricant may help 

prevent UTIs. 

Points to Remember 

• Most urinary tract infections (UTIs) 

arise from one type of bacteria, 

Escherichia coli (E. coli), which 

normally lives in the bowel. 

• Symptoms of a UTI in adults may 

include the following: 

– a frequent and intense urge to 

urinate 

– a painful, burning feeling in 

the bladder or urethra during 

urination 

– feeling tired, shaky, and weak 

– muscle aches 

– abdominal pain 

– only small amounts of urine 

passed, despite a strong urge to 

urinate 

– cloudy, dark, or bloody urine or 

urine that has a foul smell 

– pain in the back or side below 

the ribs 

– nausea and vomiting 

• Fever may indicate a kidney or prostate infection. 

• Because bacteria can be found in 

the urine of healthy individuals, a 

UTI is diagnosed based both on 

symptoms and a laboratory test. 

• UTIs are treated with bacteriafighting medications called antibiotics or antimicrobials. 

10 Urinary Tract Infections in Adults 
 

 

 

 

 

 

 

 

 

 

 

 

Hope through Research 

Scientists are working on developing a 

vaccine that can prevent UTIs from coming back. 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. Other scientists 

are working on identifying ways to prevent 

UTIs using probiotics. 

Participants in clinical trials can play a more 

active role in their own health care, gain 

access to new research treatments before 

they are widely available, and help others 

by contributing to medical research. For 

information about current studies, visit 

www.ClinicalTrials.gov. 

For More Information 

American Urological Association Foundation 

1000 Corporate Boulevard 

Linthicum, MD 21090 

Phone: 1–800–828–7866 

or 410–689–3700 

Fax: 410–689–3998 

Email: auafoundation@auafoundation.org 

Internet: www.auafoundation.org

 www.UrologyHealth.org 

The Prostatitis Foundation 

1063 30th Street, Box 8 

Smithshire, IL 61478 

Phone: 1–888–891–4200 

Fax: 309–325–7184 

Email: MCapstone@aol.com 

Internet: www.prostatitis.org 

Acknowledgments 

Publications produced by the Clearinghouse 

are carefully reviewed by both NIDDK scientists and outside experts. Betsy Foxman, 

Ph.D., University of Michigan School of 

Public Health, and Anthony Schaeffer, 

M.D., Northwestern University Medical 

School, reviewed the updated version of this 

publication. 

You may also find additional information about this 

topic by visiting MedlinePlus at www.medlineplus.gov. 

This publication may contain information about 

medications. When prepared, this publication 

included the most current information available. 

For updates or for questions about any medications, 

contact the U.S. Food and Drug Administration 

toll-free at 1–888–INFO–FDA (1–888–463–6332) or 

visit www.fda.gov. Consult your health care provider 

for more information. 

11 Urinary Tract Infections in Adults 
 

 

 

 

 

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U.S. DEPARTMENT OF HEALTH 

AND HUMAN SERVICES 

National Institutes of Health 

NIH Publication No. 12–2097 

November 2011 

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