Which of the following organisms is the most likely cause of the croup?

Examination:

The croup, a laryngotracheobronchitis, is most often caused by parainfluenza virus.

Corynebacterium diphtheriae is the cause of diphtheria, which produces laryngitis with a characteristic dirty gray membrane that may slough and be aspirated.This infection is now rare because of routine childhood immunizations.

Epstein- Barr virus is associated with infectious mononucleosis (glandular fever) and produce pharyngitis. EBV is also associated with nasopharyngeal carcinoma.

Haemophilus influenzae may cause an acute bacterial epiglottitis with an abrupt onset of pain and possible airway obstruction particularly in immunocompromised individuals.