What are the clinical manifestations of Methicillin-resistant Staphylococcus aureus (MRSA) cellulitis?

Clinical Appearance of MRSA Cellulitis

MRSA cellulitis looks essentially identical to typical streptococcal cellulitis and cannot be reliably distinguished by visual examination alone. 1

Key Clinical Features

The clinical presentation includes the following characteristics that apply to both MRSA and non-MRSA cellulitis 1:

• Rapidly spreading erythema (redness) with poorly defined borders 1
• Warmth and tenderness over the affected area 1, 2
• Swelling (edema) of the skin and subcutaneous tissues 1
• "Peau d'orange" appearance - the skin surface may resemble an orange peel due to superficial edema surrounding hair follicles, causing dimpling where follicles remain tethered to underlying dermis 1

Additional Features That May Develop

More severe presentations can include 1:

• Vesicles or bullae (fluid-filled blisters) 1
• Cutaneous hemorrhage appearing as petechiae or ecchymoses 1
• Lymphangitis (red streaking) and regional lymph node inflammation 1

Systemic Manifestations

Patients may exhibit 1, 2:

• Fever and tachycardia 1
• Confusion or altered mental status 1
• Hypotension in severe cases 1
• Leukocytosis 1

These systemic features may appear hours before visible skin changes. 1

Critical Distinction: MRSA is Rarely the Cause of Pure Cellulitis

The most important clinical point is that MRSA is an unusual cause of typical cellulitis without purulent features. 1 A prospective study demonstrated that β-lactam antibiotics (cefazolin or oxacillin) were successful in 96% of cellulitis cases, confirming that MRSA cellulitis is uncommon. 1

When to Suspect MRSA as the Cause

Consider MRSA coverage only when cellulitis is associated with specific features 1:

• Purulent drainage or exudate (this is "purulent cellulitis," not typical cellulitis) 1
• Penetrating trauma, especially from injection drug use 1
• Concurrent evidence of MRSA infection elsewhere 1
• Associated abscess that requires drainage 1
• Failure to respond to β-lactam therapy 1

Common Pitfall to Avoid

Do not assume cellulitis is caused by MRSA based on appearance alone. 1 The vast majority of non-purulent cellulitis (85%) is caused by β-hemolytic streptococci, not MRSA. 2, 3 Empirically treating all cellulitis for MRSA leads to unnecessary broad-spectrum antibiotic use. 1

Differentiating Purulent vs. Non-Purulent Presentations

• Non-purulent cellulitis: Erythema, warmth, swelling without pus or drainable abscess - streptococci are the primary cause, MRSA coverage usually unnecessary 1
• Purulent cellulitis: Cellulitis with purulent drainage, exudate, or associated abscess - MRSA should be covered empirically 1