A 17-year-old male patient ate grilled skewers from a roadside stall 2 days ago. Today, he developed chills, fever, abdominal pain, diarrhea, and tenesmus, with 5-6 bowel movements per day containing mucus. Physical examination: temperature 39°C, soft abdomen, tenderness in the left lower quadrant without rebound tenderness, active bowel sounds. Stool examination revealed mucopurulent stool, with WBC 10-15/HPF and occasional RBCs. Acute bacillary dysentery is suspected. Which of the following statements about this disease is incorrect?