A 6-year-old girl was admitted from the emergency department for evaluation and treatment of a febrile illness with a rash. The history of her chief complaint began eight days earlier when she noted a mildly painful lump in her right inguinal area. Less than 48 hours later, she noted the onset of a rash that was first noticed in the same area as the right inguinal lump but rapidly spreading in every direction.

The patient was evaluated by her primary provider, who did a complete blood count and found her white blood cell count to be 18,000 the next day. Mas...