A 20-year-old college student presented with draining sores on his right arm and back. He had a "twitchy" sensation around the lesions for 1 week. One month earlier, he returned from an extended trip to Costa Rica, where he camped in the rainforest and swam daily in the ocean. The sores developed and worsened over the past several weeks, and he was treated twice with amoxicillin-clavulanate (Augmentin). Physical examination revealed 2 nodular, indurated lesions on the right triceps and scapula, ranging in size between 1 and 2 cm, with a 1-mm opening in the apex of each lesion (Figure 1). A serosanguinous fluid was expressed on compression.

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