A 2-year-old boy is brought into the emergency room with a c…

A 2-year-old boy is brought into the emergency room with a complaint of fever for 6 days and the development of a limp. On examination, he is found to have an erythematous macular exanthema over his body, conjunctivitis, dry and cracked lips, a red throat, and cervical lymphadenopathy. There is a grade 2/6 vibratory systolic murmur at the lower left sternal border. A white blood cell count and differential show predominant neutrophils with increased platelets on smear. Which of the following is the most likely diagnosis?