A urinary tract infection (UTI) is a bacterial infection that affects any part of the urinary tract.The main causitive agent is:Escherichia coli. Although urine contains a variety of fluids, salts, and waste products, it usually does not have bacteria in it. When bacteria get into the bladder or kidney and multiply in the urine, they cause a UTI. The most common type of UTI is a bladder infection which is also often called cystitis. Another kind of UTI is a kidney infection, known as pyelonephritis, and is much more serious.

UTIs are most common in sexually active women and increase in diabetics and people with sickle-cell disease or anatomical malformations of the urinary tract. Since bacteria can enter the urinary tract through the urethra (an ascending infection), poor toilet habits (such as wiping back to front for women) can predispose to infection, but other factors (pregnancy in women, prostate enlargement in men) are also important and in many cases the initiating event is unclear.