Urinary Tract Infections (UTI)

What is Urinary Tract Infection?

Urinary tract infection (UTI) is an infection of one or more components of the urinary tract. Urinary tract is made up of two sections: the lower urinary tract and the upper urinary tract. Lower urinary tract contains the bladder and urethra. Upper urinary tract contains two kidneys and the tube that connects them, called the ureters.

Urine does not normally contain microorganisms. Most urinary tract infections are due to bacteria that enter the opening of the urethra. Bacteria stick to the walls of the urethra, multiplying and moving up the urethra to the bladder. Most UTIs remain in the lower urinary tract where they cause annoying symptoms, such as a burning sensation during urination. These infections are easily treated in most cases.

If a lower urinary tract infection is not treated, the infection may spread up through the ureters, and into the kidneys. A kidney infection is more dangerous, and can lead to permanent kidney damage. In some cases a urinary tract infection may lead to an infection in the bloodstream (sepsis, septicemia) that can be life threatening.

Some Facts About Urinary Tract Infections

  • Urinary tract infection is second only to respiratory infection as the most common type of infection.
  • Every year, urinary tract infections are responsible for nearly 10 million doctor visits.
  • About 80 to 90 percent of UTI are caused by one type of bacteria.
  • Women develop UTI much more often than men. 20% of women in the United States develop this condition and 20% of those have a recurrence.
  • Urinary tract infection is less common in men and boys than in women and girls but is more likely to be serious.
  • Men are more likely to get a UTI once past the age of 50.
  • One to two percent of children develop urinary tract infections.
  • UTI in children is more common in those under the age of 2.
  • Urinary tract infections can be treated effectively with antibiotics.

Types of UTIs

In general, the farther the organ is in the urinary tract from the place where the bacteria enter, the less likely the organ is to be infected.
Urinary tract infections include:

  • Urethritis is an infection or inflammation of the urethra. This can be due to other things besides the organisms usually involved in UTI's. In particular, many sexually transmitted diseases (STD's) appear initially as urethritis.
  • Cystitis is an infection of the bladder and is the most common form of UTI. Cystitis can often occur at the same time as urethritis. It can be aggravated if the bladder does not empty completely when you urinate.
  • Ureteritis is infection of a ureter. This can occur if the bacteria entered the urinary tract from above, or if the ureter-to-bladder valves don't work properly and allow urine to "reflux" from the bladder into the ureters.
  • Pyelonephritis is an infection of the kidney. This can happen with infection from above, or if reflux into the ureters is so bad that infected urine refluxes all the way to the kidney. Kidney infections can cause kidney damage or even failure if left untreated for an extended period of time.


Bacteria are the primary organisms that cause UTIs. Most common bacteria that cause UTIs include: Escherichia coli and Staphylococcus saprophyticus. About 80-90% of urinary tract infections are caused by Escherichia coli (E. coli). This bacterium is normally found in the digestive tract and is present on the skin around the rectal area. About 10-20% of urinary tract infections are caused by the Staphylococcus saprophyticus. Infections caused by this bacteria have a seasonal variation, with a higher incidence in the summer and fall than in the winter and spring.

And about 5% or less of urinary tract infections are caused by other bacteria. Gram-negative microorganisms causing UTIs include Proteus, Klebsiella, Citrobacter, Enterobacter, and Pseudomonas spp. Gram-positive microorganisms such as Enterococcus faecalis can also infect the urinary tract.

Microorganisms such as Chlamydia and Mycoplasma may also cause UTIs in both men and women. Unlike E. coli, Chlamydia and Mycoplasma may be sexually transmitted, and infections require treatment of both partners.

Risk factors

Risk factors for UTIs are factors that do not directly cause the disease, but seem to be associated in some way. Having a risk factor for UTIs increases the chances of getting a condition but does not always lead to UTIs.

Some factors that may contribute to urinary tract infections are:

  • Structure of the female urinary tract. In general, the women are more prone to UTIs mostly due to the shortness of the urethra, which is 1.5 inches compared to 8 inches in men. Bacteria from fecal matter can be easily transferred to the vagina or the urethra.
  • Sexual intercourse. For many women, sexual intercourse triggers an infection[1]. During sexual intercourse bacteria in the vaginal area is sometimes massaged into the urethra by the motion of the penis. Urinating after intercourse seems to decrease the likelihood of developing a urinary tract infection. Nearly 80% of all urinary tract infections occur within 24 hours of intercourse.
    It is important to note, however, that UTIs are not sexually transmitted infections.
  • Irregular urination. Infrequent visits to the bathroom can cause a woman to be more susceptible to urinary tract infections. The urine that stays in the bladder is more likely to grow bacteria and cause infections.
  • Birth control methods. Using a diaphragm for birth control, or spermicides with a diaphragm or on a condom. Women who use a diaphragm develop infections more often. If your diaphragm is not fitted properly, it may place pressure on the bladder and thus increase your chances of infection. The chemicals in spermicides may irritate vaginal tissues. Condoms with spermicidal foam may cause the growth of E. coli in the vagina, which may enter the urethra. Unlubricated condoms increase irritation and help bacteria cause symptoms of a UTI.
  • Insufficient water intake will cause less urination, which flushes out the system. Bacteria that enter the bladder have more time to multiply and to take hold, causing an infection.
  • Inadequate personal hygiene. Bacteria from anal area or vaginal discharges can enter the female urethra because its opening is very close to the vagina and anus.
  • Catheters or tubes placed in the bladder. One of the most common sources of infection is catheters, or tubes, placed in the bladder. Urinary catheterization can cause UTI by introducing bacteria into the urinary tract. The risk for developing a UTI increases when long term catheterization is required.
  • History of previous UTIs. About 80% of women with cystitis develop recurrences within two years.
  • Menopause. Studies indicate that between 20% and 25% of women over 65 years old have UTIs. In general, biologic changes due to menopause put older women at particular risk for primary and recurring UTIs. With estrogen loss, the walls of the urinary tract thin out, weakening the mucous membrane and reducing its ability to resist bacteria. Also, estrogen is essential to maintain the normal acidity of vaginal fluid.
  • Age. A man's risk for UTI increases with age. Men become more susceptible to UTIs after 50 years of age, when they are more likely to develop prostate problems.
  • Medications that lower immunity.

Health conditions that cause an increased risk for developing a UTI include:

  • Anatomical problems, such as narrowing of the urethra or ureters.
  • Urine retention - the condition when the bladder does not empty completely.
  • Vesicoureteral reflux - the abnormal flow of urine from the bladder back to the ureters.
  • Kidney disorders. Nearly any kidney disorder increases the risk for UTIs.
  • Kidney stones. In some cases, kidney stones can cause urinary tract obstruction that leads to infection, particularly pyelonephritis. Symptoms of severe urinary tract infection in people with a history of kidney stones may indicate obstruction, which is a serious condition.
  • Spinal cord injuries.
  • Diabetes causes changes to the immune system, damage to the kidneys and often results in sugar in the urine, which promotes the growth of bacteria.
  • Any condition that suppresses the immune system.
  • In men, an enlarged prostate may inhibit the flow of urine.

UTI Signs & Symptoms

The most common symptoms of a urinary tract infection involve the process of urination and are easily recognized. Symptoms of UTI may include the following:

  • The urge to urinate frequently, which may recur immediately after the bladder is emptied.
  • Painful burning sensation during urination. If this is the only symptom, then the infection is most likely urethritis, an infection limited to the urethra.
  • Discomfort or pressure in the lower abdomen.
  • Cramping in the pelvic area or back.
  • Cloudy or murky urine, which may have a strong smell. This is a very reliable indicator of urinary tract infections. Murky urine may be caused by the presence of bacteria, mucus, blood cells, or epithelial cells.
  • Fever is not common if the infection is in the lower urinary tract (urethra or bladder), but may be present, especially if the infection has spread to the kidneys.

Symptoms of kidney infections tend to affect the whole body and be more severe:

  • Increased need to urinate at night.
  • Chills and persistent fever (typically lasting more than 2 days).
  • Pain, tenderness in the flank (pain that runs along the back at about waist level).
  • Vomiting and nausea.

See also:


  • 1. Stamatiou C, Bovis C, Panagopoulos P, Petrakos G, Economou A, Lycoudt A. Sex-induced cystitis--patient burden and other epidemiological features. Clin Exp Obstet Gynecol. 2005;32(3):180-2. PubMed

Created: August 18, 2006
Last updated: February 24, 2016

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