Thanks Nitesh for your question. I'm very sorry your father in law is going through this. Infection can cause a high SUV though I don't know the value range for E coli . Oncologists usually want to get an infection under control before trying to determine if there is cancer active in that area. Tumors and infection look alike in both PET and CT. It's not often you hope for an e. coli diagnosis but when the other possibility is cancer things change.
I hope he does well, gets rid of the infection and finds no cancer. On a personal note my husbands scans never returned to normal partly because of scarring from radiation.