A kidney infection, also known as pyelonephritis, occurs when bacteria enter the kidneys, often through the urinary tract. This infection can cause symptoms such as fever, chills, back pain, and frequent urination. It is more common in women than men and can develop from untreated urinary tract infections. If left untreated, a kidney infection can lead to serious complications, including kidney damage or sepsis. Diagnosis typically involves urine tests and imaging studies. Treatment usually includes antibiotics to eliminate the infection and may require hospitalization in severe cases to ensure proper care and hydration.