77) A 14-year-old boy is brought to the emergency department for evaluation of fever and headache. The mother relates that her son has had a worsening headache for 5–6 days. She says that she took him to a walk-in clinic, and he was put on amoxicillin for a sinus infection. His headaches have been getting worse and that he is now having fevers as high as 103.6°F. The mother says that he normally is very active and that he currently has a summer job at a local park clearing out underbrush. Since he has become ill, he has had such a decrease in energy that he cannot go to work. He has had a decrease in his appetite and has been sleeping more. He denies any sore throat, abdominal pain, chest pain, dysuria, vomiting, or diarrhea. On examination, he is an uncomfortable young man whose vital signs are: temp. 101.9°F, RR 26, HR 124, and BP 79/56. His head, ear, eye, nose, and throat examination reveals normal TMs, a mildly erythematous hypopharynx, and some shotty cervical lymphadenopathy. His lungs are clear. His cardiac examination is normal. His liver edge is palpable just below the right costal margin and is mildly tender. His spleen is not palpable. His skin examination is normal with the exception of scattered petechiae around his ankles and wrists. A CBC reveals WBC 13,000 with 65% segs and 22% lymphs, hematocrit of 35, and platelet count of 95,000. His electrolytes reveal a Na 125, K 5.1, Cl 102, and bicarbonate 21. His BUN and Cr are normal.
What is his most likely diagnosis?