A 5-year-old child had acute onset of the disease with a fever of 39.5°C, marked chills, weakness, lethargy, skin pallor, and headache. Eight hours later a hemorrhagic rash developed on the skin of the buttocks and legs. The child is sluggish, the body temperature has dropped, blood pressure - 80/40 mm Hg. respiratory rate-28-30/min, diuresis is decreased. What is the most likely diagnosis in this case?