A 55-year-old man presents to the emergency department with left lower quadrant abdominal pain. The pain has been present for 1 week, but has increased in intensity over the last 2 days associated with nausea, constipation, and dysuria.
Past history is unremarkable. Examination reveals a temperature of 101°F, pulse rate of 95/min, BP of 130/70 mmHg, and normal heart and lung examinations. Abdominal examination reveals fullness and marked tenderness in the left lower quadrant, with voluntary guarding and decreased bowel sounds. Laboratory tests reveal a WBC count of 18,000 with a left shift and 20 50 WBCs in the urinalysis. A CT scan of the abdomen reveals a thickened sigmoid colon with pericolonic inflammation. He is admitted to the hospital for treatment.
Which of the following is the most appropriate management of this patient?