A 28-year-old male from Mumbai presents with sudden-onset high fever (40.5°C), severe headache, myalgia, and rash on the trunk and limbs. On day 4 of illness, he develops bleeding from gums and petechial hemorrhages. Platelet count is 45,000/μL, and NS1 antigen is positive. He denies previous dengue infection. According to NVBDCP surveillance and management protocols, what is the most appropriate immediate management step?