Most kidney infections actually begin as bladder infections and then, as the bacteria in the bladder begin to grow and multiple, climb up the tubes called the ureters which connect the kidneys to the bladder. Therefore, in order to understand the source for kidney infections, it is important to understand the source of bladder infections.
In an elderly man of 70 years, the most common reason for recurrent bladder infections, assuming your father does not routinely require the use of catheters or similar devices, would be an enlarged prostate, called benign prostatic hypertrophy, which prevents urine from clearing out of the bladder easily. Leftover urine stagnates in the bladder and makes an excellent environment for bacteria to grow. Symptoms of this problem would include difficulty initiating a urine stream, dribbling with urination, or a very weak urine stream. If your father has any of these symptoms, he should talk with his primary care doctor
or his urologist
to determine what further treatment is indicated.
Other conditions that could predispose to a frequent urinary infections or kidney infections would include multiple chronic medical problems, especially diabetes, as well as immune problems or cancer. Your father should discuss his overall health and how that may or may not related to his kidney infections with his internal medicine doctor