Symptoms and causes

Urinary tract infections don't always cause signs and symptoms, but when they do they may include:

  • A strong, persistent urge to urinate
  • A burning sensation when urinating
  • Passing frequent, small amounts of urine
  • Urine that appears cloudy
  • Urine that appears red, bright pink or cola-colored — a sign of blood in the urine
  • Strong-smelling urine
  • Pelvic pain, in women — especially in the center of the pelvis and around the area of the pubic bone

UTIs may be overlooked or mistaken for other conditions in older adults.

Urinary tract infections typically occur when bacteria enter the urinary tract through the urethra and begin to multiply in the bladder. Although the urinary system is designed to keep out such microscopic invaders, these defenses sometimes fail. When that happens, bacteria may take hold and grow into a full-blown infection in the urinary tract.

The most common UTIs occur mainly in women and affect the bladder and urethra.

  • Infection of the bladder (cystitis). This type of UTI is usually caused by Escherichia coli (E. coli), a type of bacteria commonly found in the gastrointestinal (GI) tract. However, sometimes other bacteria are responsible.

    Sexual intercourse may lead to cystitis, but you don't have to be sexually active to develop it. All women are at risk of cystitis because of their anatomy — specifically, the short distance from the urethra to the anus and the urethral opening to the bladder.

  • Infection of the urethra (urethritis). This type of UTI can occur when GI bacteria spread from the anus to the urethra. Also, because the female urethra is close to the vagina, sexually transmitted infections, such as herpes, gonorrhea, chlamydia and mycoplasma, can cause urethritis.

Urinary tract infections are common in women, and many women experience more than one infection during their lifetimes. Risk factors specific to women for UTIs include:

  • Female anatomy. A woman has a shorter urethra than a man does, which shortens the distance that bacteria must travel to reach the bladder.
  • Sexual activity. Sexually active women tend to have more UTIs than do women who aren't sexually active. Having a new sexual partner also increases your risk.
  • Certain types of birth control. Women who use diaphragms for birth control may be at higher risk, as well as women who use spermicidal agents.
  • Menopause. After menopause, a decline in circulating estrogen causes changes in the urinary tract that make you more vulnerable to infection.

Other risk factors for UTIs include:

  • Urinary tract abnormalities. Babies born with urinary tract abnormalities that don't allow urine to leave the body normally or cause urine to back up in the urethra have an increased risk of UTIs.
  • Blockages in the urinary tract. Kidney stones or an enlarged prostate can trap urine in the bladder and increase the risk of UTIs.
  • A suppressed immune system. Diabetes and other diseases that impair the immune system — the body's defense against germs — can increase the risk of UTIs.
  • Catheter use. People who can't urinate on their own and use a tube (catheter) to urinate have an increased risk of UTIs. This may include people who are hospitalized, people with neurological problems that make it difficult to control their ability to urinate and people who are paralyzed.
  • A recent urinary procedure. Urinary surgery or an exam of your urinary tract that involves medical instruments can both increase your risk of developing a urinary tract infection.

When treated promptly and properly, lower urinary tract infections rarely lead to complications. But left untreated, a urinary tract infection can have serious consequences.

Complications of a UTI may include:

  • Recurrent infections, especially in women who experience two or more UTIs in a six-month period or four or more within a year.
  • Permanent kidney damage from an acute or chronic kidney infection (pyelonephritis) due to an untreated UTI.
  • Increased risk in pregnant women of delivering low birth weight or premature infants.
  • Urethral narrowing (stricture) in men from recurrent urethritis, previously seen with gonococcal urethritis.
  • Sepsis, a potentially life-threatening complication of an infection, especially if the infection works its way up your urinary tract to your kidneys.