• Diagnosis is usually made by clinical presentation with or without Gram stain and culture
• On evaluation, location and extent of edema, erythema, warmth, and tenderness are noted so that resolution or progression may be monitored in detail
  
  • Examine for bullae, crepitus, fluctuance, necrosis, purpura, and systemic signs (eg tachycardia, hypotension)

Cellulitis

Uncomplicated

• Area involved is erythematous, warm to the touch, swollen and is distinguished from erysipelas by non-elevated,ill-defined margins
• Primarily involves the subcutaneous tissues and dermis 
• Patients are usually asymptomatic & without comorbidity

Complicated

• Cellulitis in diabetes mellitus (DM) patients including diabetic leg ulcer
• Presence of comorbidities or vascular compromise (eg peripheral vascular disease, chronic venous insufficiency, morbid obesity); if necessary, patients are hospitalized to stabilize comorbid condition
• Presence of significant systemic symptoms: Acute confusion, tachycardia, tachypnea, hypotension
• Signs of potentially severe deep soft-tissue infection: violaceous bullae, cutaneous hemorrhage, skin sloughing, gas in the tissue; surgical debridement of affected area may be required

Purulent

• Presence of purulent exudate or drainage without a drainable abscess

Nonpurulent

• Absence of purulent exudate or drainage and no abscess

Recurrent

• Cellulitis occurring 3-4 times/year even with pharmacological prophylaxis and control of predisposing factors
  
  

Gram Stain, Culture & Sensitivity

• Lesion Culture
  •  Cultures of aspirate, biopsy and blood specimens in adults without comorbid conditions yield low results and are generally not indicated
  • Essential only for those with history of malignancy, systemic complications (eg pyrexia, hypotension), predisposing factors (ie immersion injury, animal bites, neutropenia)
  • Fine-needle aspiration of closed lesions give positive results approximately 30% of the time
  • This technique may be useful when unusual pathogens are suspected (eg immunocompromised patients), when fluctuant areas are detected or when initial antimicrobial therapy failed
  • If a specimen can be taken from the site of origin of the cellulitis, positive culture can be obtained in about ¹/₃ of the patients

• Blood cultures (BC)
  
  • Useful only in patients with significant leukocytosis, severe systemic symptoms, underlying comorbidities, cellulitis complicating lymphedema, buccal or periorbital cellulitis, persistent/recurrent cellulitis, certain exposures (water- related injury or animal bites), and in the elderly or immunocompromised patient
    
    

• Unnecessary in most cases
• Computed tomography (CT) or magnetic resonance imaging (MRI) for suspected necrotizing fasciitis
• Radiographic exams may be used to rule out osteomyelitis