Orbital Cellulitis MCQ — NEET PG Practice Question | NEETPGAI
Orbital Cellulitis
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eye Ophthalmology
A 7-year-old boy presents with acute proptosis, chemosis, and ophthalmoplegia following an upper respiratory tract infection. Imaging shows orbital cellulitis with involvement of the ethmoid sinus. What is the most common bacterial organism responsible for orbital cellulitis in children?
A. Streptococcus pneumoniae
B. Staphylococcus aureus
C. Haemophilus influenzae type b
D. Pseudomonas aeruginosa
Explanation
Microbiology of Orbital Cellulitis in Children
Key Point
Staphylococcus aureus is the most common bacterial organism responsible for orbital cellulitis in children in the current era, particularly following the widespread introduction of Hib vaccination. It is also the predominant organism in post-sinusitis orbital cellulitis across most contemporary series.
Epidemiology & Risk Factors
Peak incidence: School-age children (5–10 years), though any age can be affected
Route of spread: Direct extension from paranasal sinusitis (ethmoid > maxillary > frontal > sphenoid)
Impact of vaccination: Hib conjugate vaccine (introduced in the 1990s) has dramatically reduced H. influenzae type b as a cause; S. aureus (including MRSA) has emerged as the leading pathogen
Organism Frequency in Pediatric Orbital Cellulitis (Contemporary Data)
Table
Organism
Frequency
Key Features
Staphylococcus aureus
Most common
Includes MRSA; post-sinusitis, post-traumatic, or skin-source spread
Streptococcus pneumoniae
Common
Post-sinusitis; incidence varies with PCV uptake
Streptococcus pyogenes
Less common
Group A Strep; skin/soft tissue source
Haemophilus influenzae type b
Rare (post-vaccine era)
Historically most common; now uncommon in vaccinated populations
Pseudomonas aeruginosa
Rare
Immunocompromised or post-surgical patients
High-Yield (Khurana / AAO): In the post-Hib vaccine era, S. aureus — including community-acquired MRSA — is the most frequently isolated organism in pediatric orbital cellulitis. Empiric therapy must cover S. aureus, S. pneumoniae, and anaerobes.
Why Hib Is No Longer the Answer
Prior to widespread Hib vaccination, H. influenzae type b accounted for up to 40–50% of cases.
Post-vaccination (post-1990s), its incidence has fallen dramatically to <5% in most series.
Current textbooks (Khurana's Ophthalmology, AAO Basic and Clinical Science Course) list S. aureus as the most common organism in the current era.
Clinical Pearl
The classic presentation of orbital cellulitis includes:
Fever and systemic toxicity
Rapid onset of proptosis and chemosis
Ophthalmoplegia (CN III, IV, VI involvement)
Preceding upper respiratory or sinus infection (ethmoid sinusitis most common source)
Treatment Implications
Empiric antibiotic regimen:
Vancomycin — covers MRSA and penicillin-resistant S. pneumoniae
3rd-generation cephalosporin (ceftriaxone or cefotaxime) — broad gram-positive and gram-negative coverage
Adjust based on culture and sensitivities; surgical drainage if abscess present
Warning
Always consider MRSA in children with orbital cellulitis, especially in community-acquired cases without a clear sinusitis source.
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