Urinary tract infection is a general term that refers to infections of the urogenital system by microorganisms such as bacteria, viruses, and fungi. Bacteria are the most common cause of urinary tract infections. Normally, bacteria that enter the urinary tract from the urethra are quickly removed by urination before they settle in and cause symptoms. However, sometimes bacteria outgrow the body's natural defenses and cause infection. The infection in the urethra is called urethritis, while in the bladder it is called cystitis. The urinary system has various mechanisms to prevent infections. But despite these mechanisms, infections still occur. Some bacteria have a strong ability to attach to the walls of the urinary tract and thus multiply, causing urinary tract infections. Women often suffer from urinary tract infections. Each additional episode increases the risk of recurrence (recurrent urinary tract infections), i.e. with three or more episodes of urinary tract infection each year.

The symptoms of a urinary tract infection vary with age and gender. In young women, urinary tract infections occur frequently, with burning and pain in the lower abdomen or external genitalia when urinating, and the presence of blood is not uncommon, especially at the end of urination. Older women may report weakness and abdominal pain, especially if they have a fever. Urine may look cloudy, dark, or bloody or even have an unpleasant odor. Usually, urinary tract infections do not cause a fever if only the bladder is infected.