Bacteria that enter the urethra and travel up the urinary tract are the usual cause of urinary tract infections (UTIs). Bacteria that normally live in the large intestine and are present in feces (stool) are the most common source of infection. Sexual intercourse may move bacteria into the urinary tract, especially in women. Catheters, which are small, flexible tubes inserted into the bladder to allow urine to drain, are a common source of bacterial infection in people who are in hospitals or who live in long-term care facilities.
Women who have repeated UTIs may have inherited genes that make them more likely to get these infections.