Postoperative fever at 24 hours is most commonly due to which cause?

• A. Atelectasis
• B. Urinary tract infection
• C. Deep vein thrombosis
• D. Wound infection

Answer: (B)

In the immediate postoperative period, the most likely infectious source of fever within the first 24 hours is a urinary tract infection related to perioperative catheterization. A catheter introduces bacteria into the urinary tract, and bacteriuria can provoke fever even before urinary symptoms appear, making UTI the leading infectious cause in this narrow time frame.

Atelectasis has historically been blamed for early fever, but evidence does not support it as a common cause in this window. Wound infection typically develops several days after surgery, not within 24 hours. Deep venous thrombosis can cause fever but is less common this early and usually comes with other signs such as leg swelling or tenderness.