A 7-mоnth-оld infаnt is brоught to the emergency depаrtment by а caregiver who reports that the infant has been “screaming and drawing the legs up” intermittently for the past several hours. The caregiver states the episodes seem to occur every 15–20 minutes, and between episodes the infant appears lethargic. On assessment, the nurse notes episodes of vomiting and a diaper containing dark red, jelly-like stool. Given this information, what condition does the nurse suspect?