I believe the proper way to verify your sterility level is to choose your Process Challenge Device, and infect it with a known quantity of sterility resistent bacteria. When validating the process you check the PCD' s for infection after sterilization. If they are clean you are in the clear.
Have you read EN550? It should tell you what you need to know:
"This standard specifies requirements for the development, validation, process control and monitoring of the sterilization of medical devices using ethylene oxide."