What factor primarily increases the risk of surgical site infections?

The presence of foreign material in a surgical site is a significant factor that primarily increases the risk of surgical site infections. Foreign materials, such as implants, prosthetics, or even contaminants from sutures and dressings, can serve as a nidus for bacterial colonization. When foreign bodies are introduced into sterile tissues, they can disrupt the normal healing process and provide an environment conducive to pathogen growth. Additionally, biofilms can form around these materials, further complicating any potential infection and making it harder for the immune system and antibiotics to effectively manage.

Other factors, such as patient age, type of anesthesia, and the experience of the surgeon, can contribute to overall surgical risk profiles or outcomes, but they do not have the direct, localized impact on infection risk that the presence of foreign materials does. Age can affect a patient's immune response, anesthesia types can influence procedural risks, and a surgeon's experience can minimize errors, but none of these factors fundamentally create an environment ripe for infection in the same way that foreign materials can.