Description

• An acute bacterial infection of the dermis and subcutaneous tissue
• Types and locations:
  • Periorbital: bacterial infection of the eyelid and surrounding tissues
  • Orbital: infection of the eye posterior to the septum; sinusitis is the most common risk factor.
  • Facial: often follows URI or otitis media
  • Buccal: infection of cheek in children associated with bacteremia (common before Haemophilus influenzae type B vaccine)
  • Peritonsillar: pediatric, with fever, sore throat, and muffled speech
  • Perianal: sharply demarcated, bright, perianal erythema
  • Necrotizing: gas-producing bacteria in the lower extremities; more common in diabetics

Epidemiology

• Predominant sex: male = female
• Seasonality increased hospitalizations for cellulitis in the summer with fewer in the winter months

Etiology and Pathophysiology

Cellulitis is caused by bacterial penetration through a compromise in the epidermis, the protective barrier of the skin, into the deep dermis and subcutaneous tissues.

• Microbiology
  • β-Hemolytic streptococci (groups A, B, C, G, and F), staphylococci (Staphylococcus aureus, including MRSA), and gram-negative aerobic bacilli are most common.
  • S. aureus seen in periorbital and orbital cellulitis and people who inject IV drugs
  • Pseudomonas aeruginosa seen in diabetics and other immunocompromised patients, or through nail/sharp metal puncture through soles of shoes
  • H. influenza causes buccal cellulitis.
  • Clostridia and non–spore-forming anaerobes: necrotizing cellulitis (crepitant/gangrenous)
  • Streptococcus agalactiae: cellulitis following lymph node dissection
  • Pasteurella multocida and Capnocytophaga canimorsus: cellulitis preceded by bites
  • Streptococcus iniae: immunocompromised hosts
  • Rare causes: mycobacterium, fungal (mucormycosis, aspergillosis)

Risk Factors

• Skin barrier disruption (e.g., trauma, bites, intravenous drug user [IVDU], ulcers, fissures)
• Inflammation from excoriating skin disorders or radiation therapy
• Edema due to venous insufficiency; lymphatic obstruction due to surgery or congestive heart failure
• Advanced age, male gender, diabetes, hypertension, cancer, obesity
• Dermatomycosis, tinea pedis, onychomycosis, presence of S. aureus and/or streptococci in the toe webs
• Previous episode of cellulitis
• Recurrent cellulitis:
  • Cellulitis recurrence score (predicts recurrence of lower extremity cellulitis based on presence of lymphedema, chronic venous insufficiency, peripheral vascular disease, and deep venous thrombosis)
  • Seen in patients with immunosuppression, diabetes, vascular disease, chronic kidney disease, or drug use

General Prevention

• Good skin hygiene keeping skin well hydrated to avoid dryness and cracking
• Management of edema including elevation, compression stockings, pneumatic pressure pumps
• Maintain glycemic control and proper foot care in diabetic patients.

Commonly Associated Conditions

Abscess, lymphedema, venous insufficiency, stasis dermatitis, obesity