A 2 year old

girl is brought into the emergency room because of a paroxysmal cough and

fever. She has had a runny nose and a mild, occasional cough for the past week.

She is sneezing. Her temperature is 37.8deg C. The mother says the cough is now

much worse, with coughing episodes lasting up to 1 min. She says that the child

sometimes turns "blue" when coughing and yesterday fainted following

a particularly severe episode. A physical examination reveals a very ill and

distressed child. A coughing episode began in the emergency dept and lasted for

about 30 sec. The coughing was short and rapid and ended with a high pitched sound associated with inhalation.

Significant inspiratory stridor was noted, but no other abnormal breath sounds

were noted. No dullness to lung percussion was noted. The child has no history

of immunizations. A complete blood count reveals significant lymphocytosis.

Which of the following is the most likely diagnosis for this patients

condition?