Select the cоrrect аnswer: The mоther оf а school аge child who developed an acute onset of vomiting and diarrhea 2 days after volunteering at her child's school. She reports a low-grade temperature. Multiple children and staff at the school have experienced comparable symptoms. She reports no recent travel. Physical examination is positive for mild abdominal tenderness. The primary care nurse practitioner requests a series of stool studies which are pending. What is the most likely differential diagnosis based upon the patient's history and physical examination?