A 3-day post-operative patient following an appendectomy develops a fever of 102.5°F (39.2°C). His lungs are clear, and the surgical site appears clean. He complains of dysuria. What is the most likely cause of his fever?

The correct answer to the question "A 3-day post-operative patient following an appendectomy develops a fever of 102.5°F (39.2°C). His lungs are clear, and the surgical site appears clean. He complains of dysuria. What is the most likely cause of his fever?" is Option D: Urinary tract infection (UTI).

The other options — A) Wound infection, B) Pneumonia, C) Deep vein thrombosis (DVT) — are incorrect for this USMLE Exam Prep question. As explained above: Post-operative fever on day 3 with dysuria strongly suggests a urinary tract infection (UTI), often due to catheterization. This falls under the 'Water' (UTI) cause in the '5 W's' of post-op fever.