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You are seeing a 3 year old girl who was discharged from the hospital a week ago. At that time, she presented with fever, intermittent polyarthralgias, and an evanescent salmon pink rash. She was diagnosed with new onset systemic juvenile idiopathic arthritis, treated with ibuprofen, and initially did well. She now presents with unremitting fever and rash, bruising, petechiae, gum bleeding, hepatosplenomegaly, and lethargy. Labs reveal elevated transaminases, ferritin, LDH, and triglycerides, but a low ESR.

Which of the following is the most likely diagnosis?