Kidney infection (pyelonephritis) is a type of urinary tractinfection (UTI) that generally begins in your urethra or bladder and travels to one or both of your kidneys. With a kidney infection, patients typically experience fever and flank or low to mid-back pain and tenderness. Shaking, chills, malaise, abdominal pain, nausea, and vomiting, cloudy or smelly urine can accompany kidney infection as well.