Normally, urine is sterile. It is usually free of bacteria, viruses, and fungi but does contain fluids, salts, and waste products. An infection occurs when tiny organisms, usually bacteria from the digestive tract, cling to the opening of the urethra and begin to multiply. The urethra is the tube that carries urine from the bladder to outside the body. Most infections arise from one type of bacteria, Escherichia coli (E. coli), which normally lives in the colon.
In many cases, bacteria first travel to the urethra. When bacteria multiply, an infection can occur. An infection limited to the urethra is called urethritis. If bacteria move to the bladder and multiply, 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 urinary tract infections (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.
Bacteria can gets into your urinary tract and cause a UTI in many ways:
- Wiping from back to front after a bowel movement (BM). Germs can get into your urethra, which has its opening in front of the vagina (vuh-JEYE-nuh).
- Having sexual intercourse. Germs in the vagina can be pushed into the urethra.
- Waiting too long to pass urine. When urine stays in the bladder for a long time, more germs are made, and the worse a UTI can become.
- Anything that makes it hard to completely empty your bladder, like a kidney stone.
- Having diabetes, which makes it harder for your body to fight other health problems.
- Loss of estrogen (ESS-truh-juhn) (a hormone) and changes in the vagina after menopause. Menopause is when you stop getting your period.
- Having had a catheter (KATH-uh-tur) in place. A catheter is a thin tube put through the urethra into the bladder. It's used to drain urine during a medical test and for people who cannot pass urine on their own.
Source: U.S. Department of Health and Human Services
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