Causes of Orbital Cellulitis
Primary Etiology: Sinusitis
- Sinusitis is the source in the vast majority of orbital cellulitis cases, with infection spreading from adjacent paranasal sinuses, especially ethmoid sinuses, through the thin medial orbital wall, valveless veins, or orbital foramina 1, 2, 3, 4
Common Bacterial Pathogens
- Streptococcus pneumoniae is one of the most common causative agents of orbital cellulitis 1, 2
- Nontypeable Haemophilus influenzae remains a common cause despite vaccination programs 1, 2
- Streptococcus pyogenes (Group A Streptococcus) is increasingly recognized, with rapid progression to abscess formation 1, 2
- Staphylococcus aureus (including MRSA) is a common pathogen, particularly in trauma-related cases 1, 2
- Moraxella species are frequently isolated from sinus-related infections 1, 2
- Anaerobic bacteria are present in polymicrobial infections, especially in adults 1, 2
Fungal Causes (High-Risk Populations)
- Aspergillus species are a cause of orbital cellulitis in immunocompromised patients 1, 2
- Zygomycetes (mucormycosis) are a cause of orbital cellulitis, particularly in diabetic or immunosuppressed patients 1, 2
- Maintain a high index of suspicion for invasive fungal infection in immunocompromised patients due to high morbidity and mortality 4, 5
Alternative Routes of Infection
- Direct trauma to the orbit with percutaneous introduction of pathogens is a less common cause of orbital cellulitis 3
- Hematogenous spread is a rare cause of orbital cellulitis 2
Important Clinical Distinctions
- Orbital cellulitis must be distinguished from preseptal (periorbital) cellulitis, which has different causative patterns, with preseptal cellulitis typically caused by Staphylococcus aureus or Streptococcus pyogenes following trauma or skin breaks 2