* The culprit in at least 90% of uncomplicated infections is Escherichia coli, better know as E coli. These bacteria normally live in the bowel (colon) and around the anus.
* These bacteria can move from the area around the anus to the opening of the urethra. The two most common causes of this are poor hygiene and sexual intercourse.
* Usually, the act of emptying the bladder (urinating) flushes the bacteria out of the urethra. If there are too many bacteria, this won't stop them.
* The bacteria can travel up the urethra to the bladder, where they can grow and cause an infection.
* The infection can spread further as the bacteria move up from the bladder via the ureters.
* If they reach the kidney, they can cause a kidney infection (pyelonephritis), which can become a very serious condition if not treated promptly.
at 3:06 PM on Apr. 2, 2009