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 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 (2)

Incidence
27 annual visit rates per 1,000 people for purulent SSTI in 2015 (1); 0.2 to 24.6 per 1000 person years 200/100,000 patient/years

Prevalence
Visits to U.S. ambulatory practices for purulent skin and soft tissue infection (SSTI) range from 5.4 to 11.35 million visits annually (1); 3.3 million new cases in the United States in 2012 costing $15 billion

Etiology and Pathophysiology

Cellulitis is caused by bacterial penetration through a compromise in the epidermis, the protective barrier of the skin.

• Microbiology
  • β-Hemolytic streptococci (groups A, B, C, G, and F), Staphylococcus aureus, including MRSA, and gram-negative aerobic bacilli are most common.
  • S. aureus seen in periorbital and orbital cellulitis and IV drug users
  • Pseudomonas aeruginosa seen in diabetics and other immunocompromised patients
  • 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, syphilis)

Genetics
No genetic pattern

Risk Factors

• Disruption of skin barrier: trauma, infection, insect bites, injection drug use, body piercing, maceration
• Inflammation: excoriating skin disorders or radiation therapy
• Edema due to venous insufficiency; lymphatic obstruction due to surgery or congestive heart failure (CHF)
• Elderly, diabetes, hypertension, obesity
• Tinea pedis
• 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) (3)[A]
  • 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 (3).

General Prevention

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

Commonly Associated Conditions

Abscess, lymphedema, venous insufficiency, obesity