Urine is typically sterile. An infection occurs when bacteria get into the urine and begin to grow. The infection usually starts at the opening of the urethra where the urine leaves the body and moves upward into the urinary tract. Anyone can develop a UTI, but the following can increase the likelihood of developing one:- Sexual Intercourse
- Poor personal hygiene
- People with problems emptying the bladder
- Having a urinary catheter
- Pregnancy
- Menopause
- Some forms of contraception including diaphragms
- Immobility for extended periods of time
Source: http://www.medicinenet.com/urinary_tract_infection/page2.htm