The presence of fever, tachycardia, and wound erythema in a post-operative patient strongly suggests an inflammatory response due to infection at the surgical site. These signs are classic for a surgical site infection (SSI), which occurs when bacteria invade the wound area, causing localized inflammation and systemic symptoms. Early identification is crucial to prevent progression to severe complications like abscess formation or sepsis. Other options like pulmonary embolism or deep vein thrombosis typically do not present with wound erythema. Thus, the combination of systemic signs and local wound changes supports SSI as the most likely diagnosis.

Reference: Schwartz’s Principles of Surgery, Brunicardi, 11th Edition.