The urethra is the tube that carries urine from the bladder to the outside of the body. Organisms can also enter the bladder on urinary catheters . Bacteria in the bladder are usually flushed out when the person urinates. If bacteria multiply faster than they can be removed, a UTI results. UTIs are more common in women than in men.
Women have a shorter urethra which allows easier access for bacteria.
The most common cause of a UTI is a bacteria called E. coli. These bacteria are normally present in the bowel and feces. They can be introduced into the bladder by sexual activity. Not all UTIs can be prevented. Diagnosis of a UTI begins with a medical history and physical exam.