Skin Soft Tissue Infection
1. Clinical Spectrum by Depth
Top-Down Classification:
| Epidermis | Impetigo |
| Dermis | Erysipelas, Ecthyma, Folliculitis |
| Subcutaneous | Cellulitis, Abscess, Furuncle/Carbuncle |
| Deep Fascia | Necrotizing Fasciitis (Surgical Emergency) |
2. Purulent vs. Non-Purulent
Purulent SSTI (Abscess/Furuncle)
- The Clue: Presence of fluctuance, pus, or a central "head." Usually caused by Staphylococcus aureus (including MRSA).
- Vs Non-Purulent: Requires Incision & Drainage (I&D) as the primary treatment. Antibiotics alone are often insufficient.
Non-Purulent SSTI (Cellulitis/Erysipelas)
- The Clue: Diffuse erythema, edema, and warmth without a localized collection of pus. Usually caused by Streptococcus pyogenes.
- Vs Purulent: Primarily managed with systemic antibiotics.
3. Red Flags & Referral
🚨 Refer to ED / Surgical Team if:
- Crepitus: "Crunching" sensation on palpation (suggests gas-producing organisms).
- Bullae/Necrosis: Purple/black skin discoloration or hemorrhagic blisters.
- Pain Out of Proportion: Severe pain that doesn't match the mild appearance of the skin (Key sign of Necrotizing Fasciitis).
- Rapid Progression: Rapidly expanding erythema within hours.
- SIRS: Fever >38°C, Tachycardia >90bpm, or Hypotension.
4. Management
Antibiotic Selection (7-10 Days):
- Cloxacillin: 500mg QID. Children: 12.5mg/kg QID.
- Cephalexin: 1g BD. Children: 25mg/kg BD.
- Augmentin: 625mg TDS (if bite-related or diabetic). Children: 15mg/kg TDS.
⚠️ Clinical Pearl: Elevation is as important as antibiotics. Elevate the affected limb above the level of the heart to reduce edema and improve antibiotic penetration.