Review Question - QID 109971

A 12-month-old boy is brought to the emergency department by his mother for several hours of crying and severe abdominal pain, followed by dark and bloody stools in the last hour. The mother reports that she did not note any vomiting or fevers leading up to this incident. She does report that the boy and his 7-year-old sister recently had “stomach bugs” but that both have been fine and that the sister has gone back to school. The boy was born by spontaneous vaginal delivery at 39 weeks and 5 days after a normal pregnancy. His temperature is 100.4°F (38.0°C), blood pressure is 96/72 mmHg, pulse is 90/min, respirations are 22/min. Which of the following was most likely to play a role in the pathogenesis of this patient’s disease?