An acutely ill 18-year-old female is brought to the emergency depament. The patient is febrile and markedly hypotensive, and her mental status is obtunded. Numerous petechial and purpuric hemorrhages are scattered over the trunk, and aspiration of a lesion reveals neutrophils engulfing gram-negative diplococci. Serum sodium is markedly decreased, and serum potassium is increased. Coagulation testing reveals increased prothrombin time, activated paial thromboplastin time, and fibrin-fibrinogen split products. Which of the following is most likely?