The risk factors for infection really fall into three categories: evironmental factors, host factors, and characteristics of the bacteriae themselves. The hospital and doctors do everything they can to control the environment. This includes administering antibiotics, wearing protective suits in the operating room, operating in special airflow rooms, and simply maintaining sterile conditions during surgery. The bacteriae are who they are.
On your part, you can do everything to keep your resistance high. This includes simple things such as keeping up with a good diet in the weeks up to surgery, getting plenty of rest, and avoiding possible sources of infection in the days leading up to surgery.
All that said, the risk of infection after knee surgery remains extremely low. I'm sure you'll do well. Best of Luck!
Thank you for the reassurance. The threat of infection and its possible consequences has been on my mind for some time. I will certainly do my part to be healthy and ready for surgery.