Hi, Thanks for writing in. Infection is always caused by a pathogenic organism like a bacteria. Stones in kidney causes stasis of urine and this leads to urinary obstruction. The urinary blockage acts as a favorable medium for the bacteria to multiply. Some times infection might also ascend from the urinary bladder and enter the kidneys. In severe cases the bacteria release air in the collecting system of the kidneys and cause a condition called emphysematous pyelonephritis. Doing a blood culture and sensitivity is important to know any blood borne septicemia. Similarly a urine culture and sensitivity will also help. A broad range antibiotic should be given through intravenous route. This ensures better drug delivery and at higher concentration to kill the disease causing bacteria. Most people recover in a week after starting treatment. Cancer is less likely however detailed imaging is suggested. Please do not worry.