Pyelonephritis is a type of kidney infection that occurs when bacteria travel up the urinary tract and infect one or both kidneys. It often starts as a urinary tract infection (UTI) that spreads. Symptoms may include fever, chills, back pain, and frequent urination. Treatment typically involves antibiotics to eliminate the infection. In severe cases, hospitalization may be necessary for intravenous antibiotics and fluids. If left untreated, pyelonephritis can lead to serious complications, including kidney damage or sepsis, a life-threatening response to infection. Early diagnosis and treatment are essential for a good outcome.