Question: A 9-year-old presents with a 72-hour history of multiple episodes of watery, mildly bloody stools without mucus. They have vomited approximately four times. The child's temperature has been as high as 101.2°F. The child has vague generalized abdominal cramping. Urine output has been normal. Appetite is poor, but they are taking fluids well. The child's past history is remarkable for sickle cell disease. The examination reveals normal vital signs except for a temperature of 101.0°F. Oral mucosa is slightly dry. Skin turgor is normal. Bowel sounds are slightly hyperactive. The child has generalized abdominal tenderness without guarding or rebound. Rectal examination reveals no tenderness but produces grossly bloody liquid stool. What is the most likely etiology? A. Shigella B. Campylobacter C. Norwalk virus D. Salmonella