A 34-year-old woman presents to the emergency department with acute onset severe headache, confusion, and fever (38.5°C). On examination, she has petechial rash over the lower extremities and trunk. Laboratory investigations reveal: Hb 9.2 g/dL, WBC 18,500/μL, platelets 45,000/μL, PT 18 s (normal 12–14 s), aPTT 42 s (normal 26–36 s), fibrinogen 120 mg/dL (normal 200–400 mg/dL), D-dimer >5000 ng/mL. Blood culture is pending. What is the most likely diagnosis?