Kidney infection most often occurs as a result of a bladder or urinary tract infection, but the kidneys can also be infected through the bloodstream, although it is rarer. Most infections that enter the kidneys through the bloodstream originate from another infected area of the body, such as a skin infection or from an infected foreign body, such as a hip prosthesis or an infected heart valve.
Other possible causes of kidney infection include:
Cystoscopic examinations of the bladder and urethra
Surgery on the urinary tract
Conditions that prevent the efficient flow of urine from the bladder