A 27-year-old man presents with a 2-day history of a diffuse rash, most prominent on his chest and back. He reports having receptive anal sex with several men in the last 2 months. Physical examination shows an erythematous macular rash on his chest, back, and palms. He has no visual, hearing, or neurologic complaints, and a neurologic examination is normal. A clinical diagnosis of secondary syphilis is made. Laboratory studies are ordered, and he is treated with a single intramuscular dose of 2.4 million units of benzathine penicillin G. Later, the laboratory studies return with a positive treponemal enzyme immunoassay (EIA), a Rapid Plasma Reagin (RPR) titer of 1:256, and a negative HIV-1/2 antigen-antibody test.