What microorganisms cause preseptal cellulitis?

Microorganisms Causing Preseptal Cellulitis

The most common microorganisms causing preseptal cellulitis are Streptococcus species (particularly group A Streptococcus/S. pyogenes) and Staphylococcus aureus, with increasing prevalence of community-acquired MRSA in recent years. 1, 2

Common Causative Pathogens

Primary Pathogens

• Streptococcus species - often group A (S. pyogenes), but also groups B, C, or G streptococci 1, 3
• Staphylococcus aureus - including both methicillin-sensitive and methicillin-resistant strains 1, 2
• Haemophilus influenzae B - historically common but has decreased significantly due to vaccination 4, 5
• Streptococcus pneumoniae 4
• Moraxella catarrhalis 4

Less Common Pathogens

• Proteus species - rare but documented in case reports 6
• Pseudomonas aeruginosa - particularly in immunocompromised patients 2

Pathogenesis and Risk Factors

• Preseptal cellulitis typically results from:

  • Direct trauma to the eyelid 1
  • Extension from adjacent sinusitis (particularly ethmoid sinusitis) 1
  • Preexisting skin infections such as impetigo 1
  • Insect bites or other breaks in the skin barrier 1

• Risk factors for more severe infections include:

  • Young age (more common in children) 5
  • Immunocompromised status 3
  • Diabetes 1
  • Recent trauma to the periorbital region 3

Clinical Considerations

Diagnostic Approach

• Preseptal cellulitis is distinguished from orbital cellulitis by the absence of:

  • Proptosis
  • Limitation of extraocular movements
  • Pain with eye movements
  • Visual impairment 1, 4

• Imaging (CT orbits with IV contrast) is the most useful tool to differentiate preseptal from orbital cellulitis and to detect complications 1

Treatment Implications

• Empiric antibiotic therapy should target both streptococci and staphylococci 1

• For mild cases, oral beta-lactams may be sufficient in areas where CA-MRSA is not prevalent 1

• Suitable oral agents include:

  • Dicloxacillin
  • Cephalexin
  • Clindamycin
  • Erythromycin (with caution due to increasing resistance) 1

• For more severe infections or when MRSA is suspected:

  • Consider parenteral therapy with agents effective against MRSA (vancomycin, linezolid, or daptomycin) 1
  • Step-down therapy may include trimethoprim-sulfamethoxazole or tetracyclines based on susceptibility results 1

Complications and Prognosis

• Preseptal cellulitis typically has a good prognosis with appropriate antibiotic therapy 2

• Potential complications include:

  • Progression to orbital cellulitis
  • Abscess formation
  • Lid necrosis
  • Cicatricial ectropion 2
  • In rare cases, severe complications like toxic shock syndrome (particularly with S. pyogenes) 3

• Failure to respond to initial therapy should prompt consideration of:

  • Resistant organisms
  • Abscess formation requiring drainage
  • Misdiagnosis (orbital rather than preseptal involvement) 6, 4