A urinary tract infection is an infection in any of the structures of the urinary tract. Normally, the urinary tract can defend itself against infection by flushing out non-entrenched bacteria during urination and by the work of specialized bacteria-fighting cells in the bladder mucosa. When pathogens overcome these defense mechanisms, the urinary tract becomes infected.

All together, urinary tract infections are responsible for more than 700,000 office visits and more than 100,000 hospitalizations each year in the United States. They are the most common infections occuring in nursing homes and hospitals. Urinary tract infections associated with catheters are the most common infections acquired in acute care and long term care facilities.