An 18-year-old man is rushed to the emergency room in shock following a motor vehicle accident. He is transfused with 5 U of blood. Following the transfusion the patient complains of fever, nausea, vomiting, and chest pain. Laboratory data show elevated indirect serum bilirubin, decreased serum haptoglobin, and a positive Coombs test. Which of the following is the most likely diagnosis?