A 72-year-old female with a history of diverticulosis presents with sudden onset of severe lower abdominal pain, fever, and tachycardia. Diagnostic imaging reveals extraluminal air and fluid collection in the left lower quadrant. Labs show an elevated white blood cell count and increased serum lactate. Which of the following is the BEST predictor of the need for emergent surgical intervention in this patient?
White blood cell count > 15,000 cells/µL
Presence of fluid collection on radiological studies
Localized peritonitis on physical examination
Presence of distant free intraperitoneal air on imaging