A urinary tract infection (UTI) is an infection that occurs in the urinary tract. The urinary tract includes the kidneys, bladder and urethra. The kidneys are 2 bean-shaped organs that are found beside the spine in the lower back. The most common urinary tract infections are those caused by bacteria, although they can also be caused by viruses, fungi or parasites. Many of them are responsible for the bacteria called Escherichia coli, which normally live in the intestine.
In healthy people, urine from the bladder is sterile. The duct that carries urine from the bladder to the outside of the body (urethra) does not contain bacteria either or contains very few, so it is not possible to cause infection.