Viral Infections USMLE Step 1 Practice Question

A 5-year-old previously unvaccinated boy presents to clinic with a 3-day history of fever (39.2°C), sore throat, and malaise. His mother reports a maculopapular rash that began on his face and has progressively spread to his trunk and extremities over the past 2 days. On examination, he has pharyngitis, palatal petechiae, and a finely textured erythematous rash that blanches with pressure. His tongue is beefy red with prominent papillae ('strawberry tongue'). A rapid streptococcal antigen test returns positive. The child's immunization records are unavailable. Which of the following viral exanthems is most important to differentiate from scarlet fever in this clinical scenario?