An 18-year-old male presented with diarrhea yesterday, passing 5-6 loose stools. Today, the stools became mucopurulent, occurring every 2 hours with small volume, accompanied by tenesmus. Physical examination: soft abdomen, tenderness in the left lower quadrant, and hyperactive bowel sounds. Laboratory tests: WBC 14.6×10<sup>9</sup>/L (neutrophils 86%), stool microscopy showed RBCs 20/HP, WBCs covering the entire field, and macrophages 0-1/HP. Multiple similar diarrhea cases were reported in his class this week. Clinical diagnosis: bacillary dysentery. Which of the following measures is NOT immediately required?