Review Question - QID 212579

A 3-year-old boy presents to the emergency department with a fever and a rash. This morning the patient was irritable and had a fever which gradually worsened throughout the day. He also developed a rash prior to presentation. He was previously healthy and is not currently taking any medications. His temperature is 102.0°F (38.9°C), blood pressure is 90/50 mmHg, pulse is 160/min, respirations are 17/min, and oxygen saturation is 98% on room air. Physical exam is notable for a scarlatiniform rash with flaccid blisters that rupture easily, covering more than 60% of the patient’s body surface. The lesions surround the mouth but do not affect the mucosa, and palpation of the rash is painful. Which of the following is the most likely diagnosis?