A two year old presents to the emergency department with acute onset of stridor and tachypnea.Mother states he has been well except for cold like symptoms over the past 24 hours. Past medical history is significant for prematurity, born at 28 weeks gestation. Mother is unsure of immunization status.

Vital signs include temperature 39 rectal, heart rate 160, respiratory rate 30, blood pressure 100/70. Physical exam reveals a two-year old child with marked inspiratory stridor and moderate respiratory distress. Patient is in mother's arms but becomes agitated when approached.

1. List 3-5 possible diagnoses based on the history and physical exam.
2. What additional history would be helpful?
3. What additional physical exam findings would be helpful?
4. What laboratory or radiology data would assist with the diagnosis?
5. Cite a current pediatric reference used to answer these questions.