Pyelonephritis is a type of kidney infection that occurs when bacteria travel up the urinary tract and infect one or both kidneys. It can cause symptoms such as fever, chills, back pain, and frequent urination. This condition is often a result of an untreated urinary tract infection (UTI) and can lead to serious complications if not addressed promptly. Diagnosis typically involves urine tests, blood tests, and imaging studies to assess kidney function and detect any abnormalities. Treatment usually includes antibiotics to eliminate the infection, and in severe cases, hospitalization may be necessary to manage symptoms and prevent complications.