Urinary Tract Infection

A urinary tract infection (UTI) is an infection involving any of the organs or structures of the urinary tract, including the kidneys, ureters, bladder, and urethra.

Infections of the urinary tract are the second most common type of infection in the body. According to the Centers for Disease Control, UTI's accounted for about 8.3 million doctor visits in the US in 1997.^[1] Women are especially prone to UTI's because of anatomic differences. It is estimated that one woman in five will develop a UTI some time during her lifetime. UTI's in men are not as common and can be very serious when they occur.

Anatomy of the female urinary system. Source: National Cancer Institute

The Urinary Tract

Kidneys, ureters, bladder, and urethra. Source: Wikimedia Commons

The urinary system consists of the kidneys, ureters, bladder, and urethra. The key elements in the system are the kidneys, a pair of 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, keeping a stable balance of salts and other substances in the blood. They also produce a hormone called erythropoeitin that aids in the formation of red blood cells. Narrow tubes called ureters carry urine from the kidneys to the bladder, a sack-like organ 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.

Signs and Symptoms

Not everyone with a UTI has symptoms, but most people get at least some symptoms. These may include a frequent urge to urinate and a painful, burning sensation during urination. There may be fatigue, chills, or pain without urination. Often women feel an uncomfortable pressure in their lower abdomens just 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 upon sampling may look cloudy or red if blood is present. A UTI will not cause fever if the infection is located in the bladder or urethra. A fever usually means the infection has traveled up to the kidneys to cause pyelonephritis. Other symptoms of a kidney infection include back pain 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 presents with irritability, abnormal appetite, an unexplained fever that does not go away, incontinence or loose bowels, a change in urinary pattern, or is not thriving. Unlike adults, children are more likely to have fever and no other symptoms.

Causes

Normally, urine is sterile, or free of bacteria, viruses, and fungi. It normally contains only fluids, salts, and waste products. An infection occurs when tiny organisms, usually bacteria from the digestive tract, gather at the opening of the urethra and multiply or colonize. The urethra is the tube that carries urine from the bladder to the outside of the body. The bacteria most associated with UTIs (80%) of cases is Escherichia coli (E. coli) which normally lives in the colon. Staphylococcus saprophyticus, Proteus mirabilis, and Klebsiella species account for most other cases.

In many cases, bacteriafirst travel to the urethra. When bacteria multiply, an infection can occur. An infection limited to the urethra is called urethritis. If bacteria travel to the bladder through the urethra, a bladder infection, called cystitis, results. If the infection is not treated promptly, bacteria may then travel further up the ureters to multiply and infect the kidneys. A kidney infection is called 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.

Diagnosis

Although diagnosis can in some cases be made over the phone, a urine sample is usually taken to test for pus and bacteria. This is called a urinalysis. A simpler type of urinalysis that can be performed in minutes is called a urine dipstick. It is somewhat less accurate but faster than a formal urinalysis.

For results to be accurate, the urine sample has to be as clean as possible—specifically, it is important that the urine not be contaminated by the normal bacteria that live in the genital area. A "clean catch" urine sample requires first washing the genital area (usually with moist towelettes). Women should hold the labia (lips of the vagina) apart with their fingers. Then a "midstream" sample of urine is collected in a sterile container: the person begins urinating into the toilet (this helps flush out contaminating bacteria), then pauses, then collects some urine into the container. Usually the sample is sent to a laboratory, although some doctors' offices are equipped to do the testing.

The urine is examined for white and red blood cells and bacteria. In some cases (such as pregnancy, recent antibiotic use, seven days or more of symptoms, diabetes, immune system problems, hospital-acquired infections, recent urinary tract instrumentation, or a known anatomic abnormality of the urinary tract)^[2] the bacteria are grown in a culture, where they can be identified. They can also be tested against different antibiotics to see which drug the bacteria is most susceptible. This last step is called a sensitivity test. It isn't always done because in many cases a good guess can be made regarding which antibiotic to treat with.

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. The patient's personal history also is used to determine which tests are ordered.

If an infection persists with treatment and is traced to the same strain of bacteria, the doctor may order tests to look for any anomalies in the patient's anatomy. One of these tests is an intravenous pyelogram, 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.

Patients with recurrent infections might also need 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.

Treatment

Medications

UTIs are treated with antibiotics. 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 (TMP/SMZ; Bactrim, Septra, Cotrim), amoxicillin (Amoxil, Trimox, Wymox), nitrofurantoin (Macrodantin, Furadantin), and ampicillin (Omnipen, Polycillin, Principen, Totacillin). A class of drugs called quinolones includes four drugs approved in recent years for treating UTIs. These drugs include ofloxacin (Floxin), norfloxacin (Noroxin), ciprofloxacin (Cipro), and trovafloxin (Trovan).

Often, a UTI can be fully treated with three days of treatment if the infection is not complicated by an obstruction or other disorder. Some doctors ask their patients to take antibiotics for a week or two to ensure that the infection has been cured. Single-dose treatment is available, but 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, TMP/SMZ, or doxycycline. A follow-up urinalysis is sometimes done to confirm that the urinary tract is infection-free. Patients should 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 for IV antibioticsfor a few days, until they can take fluids and oral antibiotics on their own. Kidney infections generally require several weeks of antibiotic treatment.

Therapies

Various drugs are available to relieve the pain of a UTI. One useful drug is pyridium, a type of anesthetic that can be taken for two or three days and that has the unusual side effect of turning the urine and other body fluids an orange color. A heating pad may also help. Most doctors think that drinking plenty of water helps cleanse the urinary tract of bacteria.

Holistic and alternative treatments

• Cranberry juice from the cranberry plant Vaccinium macrocarpon has long been used as a home remedy for urinary tract infections. It is thought that compounds in the juice called proanthocyanins prevent bacteria from sticking to the bladder wall, which means they wash out harmlessly in the urine. Some studies testing cranberry products for their ability to prevent urinary tract infections have shown promise. These studies have generally been small in size, and some were not randomized or controlled; therefore, the results are not conclusive. Cranberry products have not been adequately tested to see if they can be used to help treat an existing urinary tract infection.
• Arctostaphylos uva-ursi, a herb containing the compound arbutin, has been used in some traditional remedies. The optimal dosage, as well as its safety and efficacy, are not yet well-established.^[3]
• Other herbs used in UTIs, but about which little scientific information is available, include Juniperus communis (juniper) and berberine.^[3]

Complications

When treated promptly and properly, UTIs rarely lead to complications. However, untreated UTIs can lead to problems. The most common of these are acute or chronic kidney infections (pyelonephritis), which can cause permanent damage to the kidneys. The very young and very old have a higher risk of kidney damage. There is also a possible link between women who have UTIs while pregnant, and low birth weight or premature infants.

Prevention

Doctors suggest some additional steps that a woman can take to avoid an infection:

• Drinking plenty of water every day.
• Urinate as soon as the urge is felt and not waiting.
• Wiping from front to back to prevent bacteria around the anus from entering the vagina or urethra.
• Taking showers instead of baths.
• Cleaning the genitals before sexual intercourse.
• Avoiding feminine hygiene sprays and scented douches, which may irritate the urethra.

Sexual practices

Women who use a diaphragm are more likely to develop a UTI than women who use other forms of birth control. If they use spermicide, the risk is even higher. ^[4]

Sometimes women are advised to urinate shortly after having sex to reduce the chances of getting a UTI. This recommendation has been disputed and it's not clear that the practice is very helpful.^[5][4]

Cranberry juice

Based on some suggestive studies, some doctors suggest drinking cranberry juice to prevent UTIs. Most commercially available cranberry juice is mixed with sugar or grape juice, so the likeliest benefit would come from pure cranberry juice, powder, pills or other extracts. The reason cranberry juice seems to help is that cranberries contain proanthocyanidins, which are compounds that prevent E. coli from attaching to the inside wall of the bladder.^{[6] [7]} E. coli will be washed away by urine flow if it can't adhere to the wall of the urinary tract. Though promising, cranberry products have not been adequately tested to see if they can be used to help treat an existing urinary tract infection.

Probiotics and Lactobacillus

Probioticsare various strains of bacteriathat confer a health benefit. The best-known probiotics are strains of Lactobacillus that naturally inhabit the colon and vagina. Research shows that the presence and dominance of Lactobacillus in the gut and vagina are associated with a reduced risk of UTIs and bacterial vaginosis.^[8][9]

Vaccines

There is no vaccine at present for UTIs, but one may be developed to help people with recurrent UTIs. Researchers 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.

Risk Factors

Gender

Females are more prone to getting a UTI than males. Women have a shorter urethra which allow the bacteria to travel towards the bladder more quickly. For many women, sexual intercourse seems to trigger an infection, although the reasons for this linkage are unclear.

Age

In adult women, the rate of UTIs gradually increases with age. UTIs may also occur in infants, both boys and girls, who are born with abnormalities of the urinary tract, which sometimes need to be corrected with surgery. UTIs are seen less often in boys and young men.

Diseases and conditions

• Any abnormalities 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 providing an environment which increases the risk for infection.

• A common source of infection is catheters, or tubes, placed in the urethra and bladder. A person who cannot void (urinate on their own), 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 need to take special care to keep the catheter clean and remove it as soon as possible.

• Diabetics have a higher risk of UTIs because their immune system doesn't work as well as in nondiabetics.

• Disorders that suppress the immune system increase the risk of UTIs.

Special Cases

Infections in pregnancy

Pregnant women are 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 due to a widening or dilation of the ureter leading to an infection of the kidney or pyelonephritis. The ureteral dilation is due to hormonal changes and shifts in the position of the urinary tract during pregnancy due to the pregnant uterus. For this reason, many doctors recommend periodic testing of urine during pregnancy. Even the presence of bacteria in the urine without symptoms is enough to warrant treatment.

Recurrent infections

Many women suffer more frequently from UTIs. Nearly 20% of those who have a UTI will have a recurrence, and 30% of those will have yet another. Of the latter group, 80% will have recurrences.

Usually, the more recent infection stems from a strain of bacteria different from the infection before it--a separate infection. Even if several UTIs in a row are due to E. coli, slight differences in the bacteria indicate distinct infections.

Research by the National Institutes of Health (NIH) suggests that one factor behind recurrent UTIs may be the ability of the 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.

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) can ask her doctor about one of the following treatment options:

• Take low doses of an antibiotic such as TMP/SMZ or nitrofurantoin daily for six 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 (one or two 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% of UTIs when used with the first morning urine specimen and may be useful for women who have recurrent infections.

Infections in pregnancy

A pregnant woman who develops a UTI should be treated promptly to avoid pyelonephritis, 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.

Complicated infections

Complicated urinary tract infections are defined as those that occur in patients who have underlying structural, medical, or neurologic disease, as well as those with indwelling bladder catheters. Patients at risk include those who have diabetes, a bladder that doesn't empty properly, bladder or uterine prolapse, or who are pregnant. The bacteria involved in complicated UTIs are not the usual familiar ones; they may include Enterobacteriaceae, Pseudomonas aeruginosa and Acinetobacter. Mixes of bacteria may be present in one infection. Curing infections that stem from a urinary obstruction or other systemic disorders 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 are often a result of 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 have serious consequences if not treated urgently.

References

1. ↑ Ambulatory Care Visits to Physician Offices, Hospital Outpatient Departments, and Emergency Departments: United States, 1999–2000. Vital and Health Statistics. Series 13, No. 157. Hyattsville, MD: National Center for Health Statistics, Centers for Disease Control and Prevention, U.S. Dept. of Health and Human Services; September 2004. PDF
2. ↑ Hickey J. Managing lower urinary tract infections. What is the best approach? Can Fam Physician. 2000 Aug;46:1577-8. Abstract | Full Text
3. ↑ ^{3.0 3.1} Yarnell E. Botanical medicines for the urinary tract. World J Urol. 2002 Nov;20(5):285-93. Epub 2002 Oct 17. Abstract | Full Text
4. ↑ ^{4.0 4.1} Hooton TM, Scholes D, Hughes JP et al. A prospective study of risk factors for symptomatic urinary tract infection in young women. N Engl J Med. 1996 Aug 15;335(7):468-74. Abstract | Full Text
5. ↑ Beisel B, Hale W, Graves RS, Moreland J. Clinical inquiries. Does postcoital voiding prevent urinary tract infections in young women? J Fam Pract. 2002 Nov;51(11):977. Abstract | Full Text
6. ↑ Gupta K, Chou MY, Howell A, Wobbe C, Grady R, Stapleton AE. Cranberry products inhibit adherence of p-fimbriated Escherichia coli to primary cultured bladder and vaginal epithelial cells. J Urol. 2007 Jun;177(6):2357-60. Abstract
7. ↑ Sobota AE. Inhibition of bacterial adherence by cranberry juice: Potential use for the treatment of urinary tract infections. J Urol. 1984;131:1013-1016. Abstract
8. ↑ Reid G, Chan RC, Bruce AW, Costerton JW. Prevention of urinary tract infection in rats with an indigenous Lactobacillus casei strain. Infect Immun. 1985 Aug;49(2):320-4. Abstract | Full Text
9. ↑ Czaja CA, Stapleton AE, Yarova-Yarovaya Y, Stamm WE. Phase I trial of a Lactobacillus crispatus vaginal suppository for prevention of recurrent urinary tract infection in women. Infect Dis Obstet Gynecol. 2007;2007:35387. Abstract | Full Text

External Links

www.4woman.gov

American College of Obstetricians and Gynecologists

American Foundation for Urologic Disease

American Urological Association

The Prostatitis Foundation

Research

Bug’s-eye-view of urinary tract reveals E. coli genes and proteins involved in infection. University of Michigan Health System. October 25, 2004.

Biosensor Rapidly Identifies Urinary Tract Infections. National Institute of Biomedical Imaging and Bioengineering. July 25, 2006.