A surgical site infection occurs when bacteria enter through an incision made during surgery. It can lead to increased morbidity, mortality, hospital stay, and costs. There are three types - superficial, deep, and organ/space infections. Risk factors include patient comorbidities, local wound factors, and microbes. Prevention focuses on proper patient preparation, aseptic technique during surgery, and postoperative wound care. Signs of severe infection include systemic inflammatory response syndrome and sepsis, which can progress to multiple organ dysfunction syndrome and death if not properly treated.