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Causes
By Mayo Clinic staff
The urinary system is composed of the kidneys, ureters, bladder and urethra. All play a role in removing waste from your body. 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, the defenses sometimes fail. When that happens, bacteria may take hold and multiply into a full-blown infection in the urinary tract.
The most common urinary tract infections occur mainly in women and affect the bladder and urethra.
- Infection of the bladder (cystitis) is usually caused by Escherichia coli (E. coli), a species of bacteria commonly found in the gastrointestinal tract. Sexual intercourse may lead to cystitis, but you don't have to be sexually active to develop it. All women are susceptible to cystitis because of their anatomy — specifically, the close proximity of the urethra to the anus and the short distance from the urethral opening to the bladder.
- Infection of the urethra (urethritis) can occur when the gastrointestinal bacteria make the short trip from the anus to the urethra. In addition, because of the female urethra's proximity to the vagina, sexually transmitted diseases (STDs), such as herpes simplex virus, gonorrhea and chlamydia, also are possible causes of urethritis.
