Epiglottitis is most commonly caused by which organism?

• A. Haemophilus influenzae
• B. Streptococcus pneumoniae
• C. Streptococcus pyogenes
• D. Staphylococcus aureus

Answer: (A)

Epiglottitis is classically caused by Haemophilus influenzae type b. This organism is a small gram-negative coccobacillus with a polysaccharide capsule (polyribosylribitol phosphate) that makes it highly virulent and anti-phagocytic. It requires X and V factors to grow, which is why it’s cultured on chocolate agar. The Hib conjugate vaccine dramatically reduced epiglottitis due to this organism in children, so modern cases are less common, but Hib remains the most well-known cause. Other bacteria like Streptococcus pneumoniae or Staphylococcus aureus can cause epiglottitis, especially in adults, but they are less common than Hib as the etiologic agent in classic pediatric epiglottitis.