Which of the following is classified as a surgical site infection?

A surgical site infection is specifically defined as an infection that occurs in the area of the body where surgery has been performed. This type of infection can arise from bacteria entering the body during the surgical procedure, leading to complications such as inflammation, redness, and pus formation at the surgical site. Factors that can contribute to these infections include the patient's health status, the type of surgery performed, and the sterilization practices employed during the procedure.

The other options refer to various factors that can lead to infections but do not specifically define surgical site infections. For instance, infections due to pre-existing conditions typically relate to conditions that existed prior to surgery, while those acquired from non-sterile medical staff might encompass broader healthcare-associated infections, not limited to surgical environments. Additionally, infections originating from environmental sources refer to bacteria or pathogens found in the surrounding area rather than the direct aftermath of a surgical intervention. Thus, only the option that describes an infection occurring directly at the surgical site aligns with the specific definition of a surgical site infection.