Causes and Treatment of Non-Purulent Cellulitis

Microbiological Evidence

• Streptococci, particularly group A Streptococcus (S. pyogenes), are the primary causative organisms in non-purulent cellulitis, causing diffuse, rapidly spreading infection, while staphylococcal cellulitis is typically more localized 1, 2
• S. aureus, including MRSA, is more commonly associated with purulent infections such as abscesses and boils, and rarely causes erysipelas (a form of superficial cellulitis) 1, 2

Treatment Guidelines

• The American College of Emergency Physicians recommends that treatment should begin promptly with agents effective against typical Gram-positive pathogens, especially streptococci, in patients with non-purulent cellulitis 1, 2
• Empiric MRSA coverage should only be considered for patients at specific risk (e.g. athletes, prisoners, IV drug users, prior MRSA exposure) or those who fail first-line therapy 1

Common Pathogens

• S. aureus is not a typical cause of non-purulent cellulitis, but rather of purulent infections, and is the predominant pathogen in purulent infections, not non-purulent cellulitis 1, 2
• P. multocida is associated specifically with animal bites (cat or dog bites), not typical non-purulent cellulitis 3