A 5-year-old child had acute onset of the disease that manifested in body temperature up to 39.5°C, marked chills, weakness, inertness, skin pallor, and headache. 8 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 is 80/40 mm Hg, respirations are 28-30/min., diuresis is decreased. Make the provisional diagnosis: