Cellulitis
Cellulitis is an acute bacterial infection of the dermis and subcutaneous tissues, most commonly caused by Streptococcus spp. (notably group A streptococci) or Staphylococcus aureus (including MRSA). It typically presents with erythema, swelling, warmth and pain, most often on the lower limb.
Presentation ranges from mild, outpatient‑treatable infection to rapidly progressive, limb‑ or life‑threatening disease (necrotising infection, sepsis).
Management in the emergency department focuses on early recognition, assessment of severity, appropriate antimicrobial choice (guided by NICE NG141 and local formularies), and timely escalation where indicated (see NICE NG141; sepsis guidance NG253/NG254).
Key points
- Common organisms: group A streptococci and S. aureus (including MRSA); consider atypical organisms after water exposure, bites, penetrating injuries or travel (NICE NG141).
- Distinguish purulent (suggests S. aureus/abscess) from non‑purulent cellulitis (more often streptococcal); this guides need for drainage and empirical antibiotic choice.
- Mark the margin of erythema with a single‑use marker to monitor spread; note erythema may be less visible on darker skin (NICE NG141).
- Use the Class I-IV practical severity framework to guide disposition and escalation (see table below).
- For suspected sepsis or shock follow NG253/NG254 and Resuscitation Council UK guidance - do not delay resuscitation or urgent antibiotics where indicated.
Clinical features and portal of entry
- Local signs: erythema, swelling, warmth, pain or tenderness; bullae, blistering, or skin necrosis may develop.