A mother brings her 7-month old infant to the emergency room with 3 days of high fever that has persisted despite regular tylenol. She has no cough, rhinorrhea or other symptoms of an upper respiratory tract infection. She has also not had any vomiting or diarrhea. She has been acting quite fussy for the past few days and was breastfeeding normally until today where she has not wanted to eat anything. Her temperature is 39°C in the ED. The rest of her vital signs were within the normal range.

Which of the following are you considering as possible etiologies for Rebecca’s fever?