My brother has been having a lot of trouble for several years, needing reconstructive surgery after a lot of stuff got removed due to prostate cancer. He's been incontinent since, but the surgery is to fix that. Trouble is, every time he goes in for surgery, they find he has a Urinary Tract Infection (UTI) and surgery gets cancelled. A couple of years ago they went ahead with surgery and although they thought he was clear, he had an infection which became a lot worse, and they had to take it all out again, taking even more and doing even more damage.
My brother's case is not your son's case, however. My brother needs various bits of plastic put in, and for this they need a sterile field. In your son's case, the field is already contaminated and this is actually causing a lot of the infections. So there is even a chance they may go ahead anyway. However, it would be far preferable for there to be no infection. I would be surprised if he were not kept on antibiotics from now until the surgery, to ensure that infection stays away and doesn't complicate his recovery.
I had kidney surgery when I was 20. I was on long-term antibiotics from before the surgery, to months afterwards. I'd been getting repeat UTIs which were aggravated by a deformed kidney. The infection got up to my kidneys and the doctor could not be sure the infection was completely gone.
It is most important to keep infection out of the kidneys. It's harder to shift a kidney infection than a bladder infection. A kidney resembles a kitchen sponge, and trying to disinfect your kitchen sponge is almost impossible.
If the infection does get up to his kidneys, he will know about it. NOT pleasant!
Marg