A 28-year-old man without the permanent place of residence was hospitalized with the provisional diagnosis of influenza. On day 5 after the onset of the disease, a roscolar petechial rash appeared on his trunk and on the inner surfaces of the limbs. Objectively, the patient presents with the body temperature of 40°C, euphoria, facial hyperemia, redness of the sclera, tremor of the tongue, tachycardia, splenomegaly and agitation. What is the most likely diagnosis in this case?