A 28-year-old man from Chennai presents with fever, severe headache, myalgia, and rash for 5 days. He reports that the fever is continuous (not periodic). On examination, he has a petechial rash on the trunk and limbs, hepatomegaly, and a positive tourniquet test. Platelet count is 85,000/μL (down from 150,000/μL 2 days ago). Dengue NS1 antigen is positive. What is the most appropriate management according to NVBDCP guidelines for dengue hemorrhagic fever (DHF)?