A 60-year-old man with a history of gastroesophageal reflux disease (GERD) presents to the emergency department with 2 to 3 days of fever, non-bloody diarrhea, and a worsening non-pruritic rash. He recently traveled to Mexico on a cruise where he ate some local food and may have been bitten by mosquitos. He denies vomiting or abdominal pain, and a review of his other systems is otherwise normal.
Vitals signs are all normal except for an oral temperature of 101.8° F. His eyes are clear, and his oropharynx is moist without lesions. His heart and lungs are normal to auscultation, and his abdomen is benign without tenderness. He has an impressive rash that is most severe on his legs and is non-blanching (see image).
Complete blood count, Chem7, and liver function test are all normal. C-reactive protein and erythrocyte sedimentation rate (ESR) were both elevated at 82 and 61, respectively.
What is the most likely cause of this rash?
What additional testing might be useful?
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