Urinary tract infection. Conceptual computer artwork of bacteria (green) in the urinary tract (represented by metal tubes). The urinary tract is usually sterile, therefore the presence of any microorganism is termed a urinary tract infection (UTI). If the bladder is inflamed it is called cystitis and if one or both kidneys are involved it is called nephritis. Women are more prone to UTIs as their urethra (tube that carries urine to the outside of the body) is shorter. Treatment is with antibiotics.