Causative Microorganisms and Treatment of Preseptal Cellulitis

Common Causative Pathogens

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
Streptococcus species, often group A (S. pyogenes), but also groups B, C, or G streptococci, are common causative pathogens 2
Staphylococcus aureus, including both methicillin-sensitive and methicillin-resistant strains, is a common causative pathogen 1

Preseptal cellulitis typically results from direct trauma to the eyelid 2
Preseptal cellulitis can result from extension from adjacent sinusitis (particularly ethmoid sinusitis) 3
Preseptal cellulitis can result from preexisting skin infections such as impetigo 2
Preseptal cellulitis can result from insect bites or other breaks in the skin barrier 2
Diabetes is a risk factor for more severe infections 2

Preseptal cellulitis is distinguished from orbital cellulitis by the absence of proptosis 3
Preseptal cellulitis is distinguished from orbital cellulitis by the absence of limitation of extraocular movements 3
Preseptal cellulitis is distinguished from orbital cellulitis by the absence of visual impairment 3
Imaging (CT orbits with IV contrast) is the most useful tool to differentiate preseptal from orbital cellulitis and to detect complications 3
Empiric antibiotic therapy should target both streptococci and staphylococci 2, 4
For mild cases, oral beta-lactams may be sufficient in areas where CA-MRSA is not prevalent 4
Suitable oral agents include Cephalexin 5 and Clindamycin 5
Suitable oral agents include Erythromycin (with caution due to increasing resistance) 2, 5
For more severe infections or when MRSA is suspected, consider parenteral therapy with agents effective against MRSA (vancomycin, linezolid, or daptomycin) 4, 6
Step-down therapy may include trimethoprim-sulfamethoxazole or tetracyclines based on susceptibility results 6
Failure to respond to initial therapy should prompt consideration of resistant organisms 6
Failure to respond to initial therapy should prompt consideration of abscess formation requiring drainage 4