Review Question - QID 212438

A 24-year-old man presents to his primary care provider with complaints of 2 days of profuse diarrhea. He states that his stool started to turn watery and lighter in color beginning yesterday, and he has not noticed any fevers. His diarrhea episodes have become more frequent and white-colored over the past day. He has also noticed dry mouth symptoms and darker urine today. He is otherwise healthy but recently returned from a trip with friends to South Asia. None of his friends have reported any symptoms. On exam, his temperature is 98.6°F (37.0°C), blood pressure is 110/68 mmHg, pulse is 80/min, respirations are 14/min. The patient has normal skin turgor, but he has noticeably dry oral mucosa and chapped lips. The patient has dull abdominal aching but no tenderness to palpation. The stool is found to contain large quantities of comma-shaped organisms. Fecal occult blood testing is negative and no steatorrhea is found. The provider recommends immediate oral rehydration therapy. Which of the following is the likely mechanism of this patient’s diarrhea?