A 2-year-old child is brought with high fever (39.5°C), drooling, severe odynophagia, respiratory distress, and 'tripod position.' Stridor is present. Lateral neck X-ray shows thumb-sign epiglottis. Which bacteria is the MOST LIKELY causative organism and the KEY virulence mechanism?

• A Haemophilus influenzae type b (Hib) with polysaccharide capsule ✓
• B Streptococcus pyogenes producing streptolysin O
• C Staphylococcus aureus producing Panton-Valentine leukocidin
• D Parainfluenza virus type 1 with neuraminidase activity

Explanation

Acute epiglottitis in unvaccinated pre-school children is classically caused by Haemophilus influenzae type b (Hib). The polyribose ribitol phosphate (PRP) polysaccharide capsule is the key virulence factor, enabling the organism to resist phagocytosis and cause invasive disease. Hib conjugate vaccine has dramatically reduced its incidence. The presentation — drooling, tripod posture, rapid progression, thumb sign — is essentially diagnostic and mandates emergent airway management before any investigation.

Reference: Ghai Essential Pediatrics, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.