Pyelitis is a urinary tract infection that affects the renal pelvis, which is responsible for filtering and transferring urine from the kidneys to the bladder. Other terms that can be used to describe pyelitis include renal pelvic inflammation, pyelonephritis, or kidney infection. These terms all refer to inflammation of the kidneys, and they have similar symptoms such as fever, chills, back pain, and pain during urination. Pyelitis can be caused by bacteria, and it often requires treatment with antibiotics. If left untreated, the infection can potentially lead to more severe health complications such as kidney damage or sepsis.