A kidney infection is one of the many different types of infection of the urinary tract. A kidney infection, sometimes referred to as pyelonephritis, is an upper urinary tract infection, in contrast to infections of the bladder and urethra, which are considered to be lower urinary tract (closer to the site of urine output) infections. A kidney infection can occur when a lower urinary tract infection spreads upward in the urinary tract to involve the kidneys. Some of the general symptoms of urinary infection can accompany kidney infection, like pain on urination (dysuria), needing to urinate frequently (urinary frequency), and feeling a strong urge to urinate (urinary urgency). 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 can accompany kidney infection as well. In more severe cases, or in elderly patients, symptoms can include low blood pressure, dehydration, rapid heart rate, and confusion.