Maths : Data Interpretation

Read the passage given below, study the graph that follows and answer the question.

During a party, a person was exposed to contaminated water. A few days later, he developed fever and loose motions. He suffered for some days before going to a doctor for treatment. On starting the treatment, he soon became better and recovered completely a few days later. The following graph shows different phases of the person's disease condition as regions A, B, C, D and E of the curve.

Which region of the curve indicates that the treatment yielded effective relief?