MSFinals-6500

A 45-year-old man is recovering on the surgical ward three days after a laparotomy and right hemicolectomy for cancer. You are asked to see him as he has developed a temperature of 38.5ºC and is tachycardic at 120 bpm and tachypnoeic at 25 breaths per minute. On examination his abdomen is soft and not distended but tender around his midline wound. There is some discharge seeping through the dressing. His chest is clear and he has no signs of a deep vein thrombosis.
What is the most probable cause of this man’s elevated temperature?