A 35 years old man presents with a 2-day history of rapid-onset severe ear pain and fullness. The patient complains of otorrhea and mild decreased hearing, which he reports began after swimming. On examination he is afebrile and the external ear canal is diffusely swollen and erythematous. He has tenderness of the tragus and pain with movement of the auricle. The tympanic membrane is only partially visualized due to the swelling. What is the most likely diagnosis?