cellulitis
Summary
Cellulitis is a bacterial infection of the deep dermis and subcutaneous tissue, most commonly caused by Streptococcus pyogenes and Staphylococcus aureus. It presents as spreading erythema, warmth, swelling, and tenderness without a defined border, distinguishing it from erysipelas.
Detail
Cellulitis is an acute bacterial infection involving the deeper layers of skin (dermis and subcutaneous fat) that spreads along tissue planes. The most common causative organisms are beta-hemolytic streptococci (especially S. pyogenes) and S. aureus, though MRSA is increasingly prevalent. Risk factors include skin breaks (trauma, surgical wounds, insect bites), immunocompromise, diabetes, lymphedema, and venous insufficiency. Clinical presentation includes erythema, edema, warmth, and tenderness that spreads without well-defined borders. Systemic symptoms may include fever, chills, and malaise. Diagnosis is primarily clinical, though blood cultures may be positive in severe cases. Treatment involves antibiotics: oral for mild cases (cephalexin, clindamycin) or IV for severe cases (vancomycin for MRSA coverage, ceftriaxone for streptococci). Complications include necrotizing fasciitis, bacteremia, and abscess formation. The condition must be differentiated from erysipelas (more superficial, well-demarcated borders) and necrotizing fasciitis (rapidly spreading, severe systemic toxicity).
Sources
- Harrison's Principles of Internal Medicine
- Fitzpatrick's Dermatology
- IDSA Clinical Practice Guidelines
- First Aid for USMLE Step 1
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