A kidney infection, also known as pyelonephritis, occurs when bacteria enter the kidneys, often through the urinary tract. This type of infection can cause symptoms such as fever, chills, back pain, and frequent urination. It is more common in women than men and can result from untreated urinary tract infections (UTIs). If left untreated, kidney infections can lead to serious complications, including kidney damage or sepsis. Treatment typically involves antibiotics to eliminate the infection. In severe cases, hospitalization may be necessary for intravenous antibiotics and fluids to help the body recover.