A 26-year-old woman presents with a 3-week history of bloody diarrhea. The blood is fresh and mixed in the liquid stool. Initially, she thought that she might have food poisoning, but could not recall eating anything unusual and had eaten the same food as her unaffected partner. Examination of abdomen revealed tenderness of left lower quadrant. Laboratory test revealed mild anemia (9g/dL) and she has mild fever too (100°F).

What is the most likely diagnosis? What immediate medication should be started? What are the further diagnostic test advised to confirm the diagnosis? *This case is from Docplexus Editorial Team for educative purpose only.