False colour scintigram (gamma camera scan) of human kidneys affected by bilateral pyelonephritis, a bacterial infection (commonly caused by Escherichia coli) of the substance of the kidneys and the renal pelvis, the section linking each kidney with the ureter (the tube connecting each kidney with the urinary bladder). Symptoms of acute pyelonephritis include low back pain, fever and weight loss; in chronic disease the kidneys become small and scarred, and kidney failure may develop. Treatment is with an appropriate antibiotic.