Review Question - QID 109814

A 2-year-old boy is brought to the pediatrician for recurrent nosebleeds. The boy was adopted two months ago and the parents have no record of his medical or family history. They report that the child has had frequent prolonged nosebleeds several times per week. Despite them applying pressure on the distal aspect of the nares and keeping his head elevated, the bleeding generally continues for hours. On exam, the boy appears pale and lethargic. A blood sample is obtained but the child bleeds through multiple pieces of gauze. No agglutination is observed when ristocetin is added to the patient’s blood. The addition of normal plasma to the sample still does not lead to agglutination. This patient has a condition that is most consistent with which of the following modes of transmission?