The child was admitted with a fever and lethargy. The admitting diagnosis was "rule out sepsis". When admitted, he was responsive but lethargic. The physical examination was within normal limits except for the left eardrum, which was reddened. He was placed on intravenous antibiotics after the full septic workup was complete. Improvement was evident by the next day, when he was alert, active, and started on feedings. He became afebrile and was discharged on oral antibiotics for otitis media, with sepsis ruled out. Required:
Find the principal diagnosis to the disease.