An unimmunized, 2-year-old boy presents with drooling from the mouth, elevated temperature, and enlarged tonsils. During attempts at intubation, no gray-white membrane is observed but the epiglottis appears "beefy" red and edematous. Which of the following is the most likely organism?

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, especially since approval of the type b vaccine. Haemophilus haemolyticus is a hemolytic variant of H. influenzae which that only occasionally causes disease. Klebsiella pneumoniae is present in about 5% of individuals and causes about 1% of pneumonias. Treponema pneumoniae is a prominent cause of pneumonia in persons 5 to 20 years old. Neisseria meningitidis can be part of the oral flora but is significant in disease when it enters the bloodstream and CNS.