A surgical site infection (SSI) occurs at the site of a surgical incision. Germs can get into the incision area, and cause an infection. It can develop within 30 days of an operation, or sometimes even up to one year if an implant (such as a knee or hip joint implant) is used. Infections can be minor, or occasionally they can increase complications that result in a longer length of stay in the hospital, or an increased readmission rate for patients. Post-operative SSIs are the most common health care-associated infections in surgical patients.