Read the following text for questions 11-15.

Dear Linda,

    Hello, Linda, how are you? It's been a long time since the last time we met. Well, I just wanted to tell you how you and your family are feeling this whole time. I hope all of you is healthy. By the way, the sad news from is that I was in a hospital last week. Based on the doctor diagnoses, I was infected by typhus.

    At first, when I was studying mathematics in the classroom, I felt my body became weaker each hour then I fainted. Then, I immediately was taken to the hospital because of the high fever.

    At the hospital, when I was brought into the emergency unit, the doctor immediately gave some treatment to make sure that I am okay. Finally, I had to stay there for four weeks. Every day the doctor kept me on a drip.

    At the third week, my condition was getting better. After the final check, the doctor gave me permission to go home. Now, I'm okay and because of my illness, I am now more careful about my food and eating time management, I don't want to get typhus again. That's all from me I guess, write to me soon, OK?

Regards,

Mirza

What is the topic of the letter above?