What is cellulitis?

Cellulitis: Definition, Diagnosis, and Management

Cellulitis is an infection of the deep dermis and subcutaneous tissue, presenting with expanding erythema, warmth, tenderness, and swelling. 1 It represents a significant global health burden with more than 650,000 hospital admissions annually in the United States alone, accounting for approximately $3.7 billion in ambulatory care costs.

Clinical Presentation and Diagnosis

Cellulitis typically presents with:

• Acute onset of redness (erythema)
• Warmth
• Swelling
• Tenderness and pain in the affected area
• Possible systemic symptoms like fever or chills

The diagnosis is primarily clinical, based on history and physical examination, as there is no gold standard diagnostic test 2. Important distinctions in presentation include:

• Classic erysipelas: Bright red erythema with tongue-like extensions, early systemic symptoms, caused by beta-hemolytic streptococci 3
• Limited cellulitis: Darker red hue, may not have early fever/chills, often associated with wounds or trauma, frequently caused by S. aureus 3

Causative Organisms

In approximately 85% of cellulitis cases, the causative bacteria cannot be cultured. Of the 15% where organisms are identified 1:

• Most cases are due to β-hemolytic Streptococcus and Staphylococcus aureus
• Less commonly, other organisms like Proteus mirabilis may cause cellulitis, particularly in patients with compromised tissue or when standard treatments fail 4

Common Mimics (Differential Diagnosis)

Several conditions can mimic cellulitis, including:

• Venous stasis dermatitis
• Contact dermatitis
• Deep vein thrombosis
• Panniculitis
• Eczema
• Lymphedema
• Erythema migrans 5, 2

Treatment Approach

Antibiotic Selection

For uncomplicated, non-purulent cellulitis, treatment should be directed against Streptococcus and methicillin-sensitive S. aureus with oral antibiotics such as penicillin, amoxicillin, or cephalexin. 2

First-line treatment options include:

• Cephalexin: 500 mg 3-4 times daily for 5-6 days 6
• Clindamycin: 300-450 mg orally three times daily for 5-6 days (especially good for penicillin-allergic patients) 6, 7
• Amoxicillin-clavulanate: 875/125 mg twice daily orally for 5-6 days 6

For more severe infections requiring inpatient management:

• Vancomycin: 15 mg/kg IV every 12 hours 6
• Linezolid: 600 mg IV/PO every 12 hours 6

Special Considerations

• MRSA coverage: Generally not recommended for non-purulent cellulitis unless specific risk factors are present (athletes, children, men who have sex with men, prisoners, military recruits, residents of long-term care facilities, prior MRSA exposure, IV drug users) 1
• Treatment duration: 5 days is typically sufficient, with extension if symptoms are not improved 1
• Pediatric patients: Avoid doxycycline in children under 8 years due to risk of dental staining 6
• Pregnant patients: Avoid doxycycline; use alternative antibiotics 6
• Immunocompromised patients: May require broader coverage 6

Management of Treatment Failure

If no improvement is seen after 72 hours of appropriate antibiotic therapy:

1. Reassess the diagnosis (consider mimics)
2. Consider resistant organisms
3. Evaluate for underlying complicating conditions (immunosuppression, chronic liver disease, chronic kidney disease) 1
4. Obtain cultures when possible to guide targeted therapy 4

Prevention of Recurrence

Addressing predisposing factors is crucial to prevent recurrence:

• Treat underlying skin conditions
• Manage edema and venous insufficiency
• Improve hygiene practices
• Consider decolonization for recurrent MRSA infections 6

Good personal hygiene practices, including daily change of socks and careful drying between toes after showers, can help prevent skin infections 6.