A 12-year-old girl is evaluated for a painless rash, which first developed a day earlier. She has no fevers, chills, otalgia, or rhinorrhea. Her medical and family history are unremarkable. She recently returned from visiting her grandparents in a rural New England town. Physical examination is notable for a rash, as shown in the image below. Which of the following is the most appropriate treatment? A. Azithromycin 10mg/kg once daily B. Doxycylcine C. Cephalexin 50mg/kg/day in 2 divided doses D. Ceftriaxone 75mg/kg once daily