What is the most common bacterial cause of orbital cellulitis in children?

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

Answer: (A)

Haemophilus influenzae was the classic leading cause of orbital cellulitis in children because this bacterium commonly colonizes the nasopharynx and can spread from infected sinuses into the orbit through the thin lamina papyracea. Before widespread Hib vaccination, Hib was the most frequent pathogen in pediatric orbital cellulitis, especially in younger kids with ethmoid sinusitis. The vaccine dramatically reduced Hib infections, shifting the relative frequency toward other organisms in modern practice, but historically it was the top culprit. Staphylococcus aureus and Streptococcus species are important causes as well, and Pseudomonas is less typical in otherwise healthy children.