The urinary tract refers to the connected system of organs through which urine flows on its way out of the body. This includes the two kidneys, the two ureters (tubes that connect the kidneys to the bladder), the bladder, and the urethra (the tube from the bladder through which urine leaves the body). A urinary tract infection can affect any or all of these structures, although a kidney infection (pyelonephritis) is generally discussed as a separate condition.

The Urinary Tract
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A urinary tract infection usually occurs when bacteria on the skin or in the genital or rectal area enter the urinary tract via the urethra. If conditions are right, these bacteria can multiply within the urethra and bladder, causing infection. Sometimes infections begin during a medical procedure that requires placement of a catheter, a thin flexible tube that is inserted through the urethra and into the bladder, to drain urine. Some organisms can “climb” up the catheter into the bladder, resulting in a urinary tract infection. Sexual intercourse is another common trigger of urinary tract infections.

Many different kinds of bacteria can cause urinary tract infections, including:

  • Escherichia coli
  • Staphylococcus saprophyticus
  • Enterococci
  • Pseudomonas aeruginosa

Viruses can cause urinary tract infections in children.

On rare occasions, fungi may cause urinary tract infections.

Twenty percent of all women will have a UTI at some point in their lives. Men, throughout most of their adult lives, have a very low rate of urinary tract infections. Over the age of 50, however, their rate of infection reaches approximately that of women because prostate enlargement predisposes men to infection. This is due to incomplete emptying of the bladder that results in urine sitting in the bladder and bacteria growing. Researchers estimate that about 8 to 10 million visits to the doctor each year are for diagnosis and treatment of urinary tract infections.