Description

• An acute bacterial infection of the dermis and subcutaneous tissue
• Types and locations:
  • Periorbital cellulitis: bacterial infection of the eyelid and surrounding tissues
  • Orbital cellulitis: infection of the eye posterior to the septum; sinusitis is the most common risk factor.
  • Facial cellulitis: preceded by upper respiratory infection or otitis media
  • Buccal cellulitis: infection of cheek in children associated with bacteremia (common before Haemophilus influenzae type B vaccine)
  • Peritonsillar cellulitis: common in children; associated with fever, sore throat, and “hot potato” speech
  • Perianal cellulitis: sharply demarcated, bright, perianal erythema
  • Necrotizing cellulitis: 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

Incidence
1.5 to 24.6 per 1,000 person years with recurrent cellulitis with an incidence rate ranging from 16% to 53% within 3 years.

Prevalence
Visits to U.S. ambulatory practices for purulent SSTI range from 5.4 to 11.3 million visits annually.

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
  • H. influenzae 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)

Genetics
No genetic pattern

Risk Factors

• Disruption of skin barrier from trauma, infection, insect bites, injection drug use, body piercing, maceration, ulcerations, chronic wounds, fissured toe webs
• 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)
  • Recurrent cellulitis is seen in immunocompromised patients (HIV/AIDS), steroids and TNF-α inhibitor therapy, diabetes, hypertension, cancer, peripheral arterial or venous diseases, chronic kidney disease, dialysis, IV or SC 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