A hyperemic edema of the larynx and epiglottis that rapidly leads to respiratory obstruction in young children is most likely to be caused by

Haemophilus influenzae is a Gram-negative bacillus. In young children, it can cause pneumonitis, sinusitis, otitis, and meningitis. Occasionally, it produces a fulminative laryngotracheitis with such severe swelling of the epiglottis that tracheostomy becomes necessary. Clinical infections with this organism after the age of 3 years are less frequent.