Cellulitis is an acute bacterial infection of the dermis and subcutaneous tissue presenting with warmth, erythema, edema, and tenderness; erysipelas is a more superficial variant with raised, sharply demarcated borders, typically caused by β-hemolytic streptococci. S. aureus (including MRSA) and streptococci are common pathogens; animal bites introduce Pasteurella, and water exposure suggests Vibrio/Aeromonas. Diagnosis is clinical; routine cultures are often low yield. Management is risk-stratified: oral anti-streptococcal agents for nonpurulent cases without systemic signs; MRSA-active agents for purulent infections or specific risks; IV therapy for severe/systemic illness. Preventing recurrence focuses on edema management, skin barrier repair, and addressing tinea pedis or interdigital maceration.
Epidemiology and Risk Factors
- Common in adults; lower extremities most often.
- Risk factors: breaks in skin (tinea pedis, ulcers, wounds), chronic edema/lymphedema, venous insufficiency, obesity, diabetes, prior cellulitis, eczema, immunosuppression.
Clinical Features
- Cellulitis: ill-defined erythema, warmth, swelling, tenderness; may have fever/chills.
- Erysipelas: abrupt onset, raised well-demarcated erythema with peau d’orange, often face or lower legs; systemic symptoms more common.
- Purulent infections suggest S. aureus; nonpurulent more likely streptococcal.
- Consider mimics: stasis dermatitis, contact dermatitis, gout, DVT, acute lipodermatosclerosis.
Diagnosis and Workup
- Clinical diagnosis; cultures from intact skin are not useful.
- Obtain cultures from purulent drainage/abscesses; consider blood cultures if severe systemic illness, immunosuppressed, animal bites, water exposure, or unusual settings.
- Labs/imaging: CBC, CRP if severe; ultrasound to detect occult abscess; MRI if concern for necrotizing infection.
Management
- Determine severity and purulence
- Nonpurulent, mild (no systemic signs): target streptococci.
- Purulent or with abscess: incision and drainage; consider MRSA coverage.
- Outpatient oral regimens (typical durations 5–7 days, extend if slow response)
- Nonpurulent: penicillin VK, amoxicillin, cephalexin, or dicloxacillin.
- β-lactam allergy: clindamycin.
- Purulent or MRSA risk (prior MRSA, IVDU, penetrating trauma, failed therapy): TMP-SMX or doxycycline; add β-lactam (e.g., amoxicillin) for streptococcal coverage if using TMP-SMX/doxycycline alone.
- Inpatient/IV regimens
- Moderate–severe nonpurulent: cefazolin, ceftriaxone, or clindamycin.
- Severe or MRSA risk: vancomycin; alternatives include daptomycin, linezolid (monitor for myelosuppression/serotonin syndrome), or ceftaroline.
- Necrotizing infection suspicion (pain out of proportion, bullae, crepitus, rapid progression, systemic toxicity): urgent surgical consult; broad-spectrum coverage (vancomycin + piperacillin-tazobactam or carbapenem) and source control.
- Special exposures
- Animal/human bites: amoxicillin-clavulanate; alternatives for allergy (doxycycline + metronidazole, or moxifloxacin).
- Freshwater: Aeromonas—fluoroquinolones.
- Saltwater: Vibrio vulnificus—doxycycline + third-generation cephalosporin.
- Recurrence prevention
- Treat interdigital tinea pedis; daily foot care and drying of toe webs.
- Manage edema/lymphedema with compression, elevation, weight management.
- Skin care: emollients, treat eczema/cracks; nail care.
- Consider prophylactic penicillin (e.g., penicillin VK 250 mg bid) for frequent recurrences after risk-factor control.
- Patient education and follow-up
- Outline erythema to monitor progression; reassess within 48–72 hours.
- Expect initial worsening in first 24 hours due to inflammation after antibiotics; ensure adherence.
References (recent guidelines and key reviews)
- IDSA guidelines for skin and soft tissue infections, updates 2021–2024.
- Trials on MRSA-active vs β-lactam therapy by purulence status, 2021–2024.
- Recurrence prevention strategies and lymphedema management literature, 2022–2024.