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Cellulitis

Basics

  • Acute bacterial infection of skin and subcutaneous tissue.
  • Types: periorbital, orbital, facial, buccal, peritonsillar, perianal, necrotizing cellulitis.
  • High health care burden with >650,000 US admissions yearly.

Epidemiology

  • Equal in males and females.
  • Incidence: 1.5 to 24.6 per 1,000 person-years.
  • Recurrent cellulitis common (16-53% within 3 years).
  • Purulent SSTI visits 5.4 to 11.3 million/year in US.

Etiology and Pathophysiology

  • Bacterial entry via skin barrier disruption.
  • Common pathogens:
  • β-Hemolytic streptococci (groups A, B, C, G, F)
  • Staphylococcus aureus (including MRSA)
  • Pseudomonas aeruginosa (diabetics/immunocompromised)
  • Haemophilus influenzae (buccal cellulitis)
  • Clostridia (necrotizing cellulitis)
  • Others: Pasteurella, Capnocytophaga (animal bites), Streptococcus iniae (immunocompromised).
  • No known genetic pattern.

Risk Factors

  • Skin barrier disruption: trauma, bites, insect bites, IVDU, ulcers.
  • Edema from venous insufficiency, lymphatic obstruction.
  • Chronic wounds, fungal infections.
  • Diabetes, hypertension, obesity, cancer, older age.
  • Previous cellulitis episodes.
  • Immunosuppression.

Prevention

  • Good skin hygiene and hydration.
  • Manage edema with elevation, compression.
  • Glycemic control and foot care in diabetics.

Associated Conditions

  • Abscess, lymphedema, venous insufficiency, stasis dermatitis.

Diagnosis

History

  • Skin barrier disruption history.
  • Local pain, itching, burning.
  • Systemic symptoms: fever, chills, malaise.

Physical Exam

  • Localized erythema, swelling, tenderness, warmth.
  • Poorly demarcated borders.
  • Lymphangitis, lymphadenopathy.
  • Purulent drainage if abscess present.
  • Orbital cellulitis: proptosis, ocular movement limitation.
  • Facial cellulitis: malaise, vomiting, pruritus.

Differential Diagnosis

  • Toxic shock syndrome, venous stasis dermatitis, DVT, thrombophlebitis.
  • Bursitis, dermatitis, herpes zoster, osteomyelitis.
  • Malignancy, drug reaction, insect bites, erythema nodosum.

Diagnostic Tests

  • Labs if systemic signs: CBC, blood cultures, CRP, ESR, CPK, lactate.
  • Swab cultures if purulence.
  • Imaging: X-ray, CT, MRI for suspected deep infection or osteomyelitis.
  • Ultrasound for abscess.
  • Gallium-67 scan for cellulitis on lymphedematous limbs.

Treatment

General Measures

  • Immobilization and elevation of affected limb.
  • Cool compresses or sterile saline dressings.
  • Compression therapy for edema.
  • Mark erythema borders to monitor progression.
  • Tetanus prophylaxis if indicated.

Medication

Nonpurulent Cellulitis (likely streptococcal/MSSA)

  • Oral (mild cases): cephalexin, dicloxacillin, or clindamycin.
  • IV (severe/rapid progression): cefazolin, oxacillin, nafcillin, or clindamycin.

Purulent Cellulitis (likely CA-MRSA)

  • Incision and drainage of abscess mandatory.
  • Oral antibiotics: TMP-SMX, clindamycin, doxycycline, minocycline, or newer agents.
  • IV antibiotics: vancomycin, daptomycin, linezolid, tedizolid, ceftaroline, tigecycline.

Necrotizing Cellulitis

  • Broad-spectrum IV antibiotics covering aerobes, anaerobes, and MRSA.
  • Ampicillin-sulbactam or piperacillin-tazobactam + ciprofloxacin + clindamycin.
  • Urgent surgical consultation.

Special Exposures

  • Freshwater: penicillinase-resistant penicillin + gentamicin or fluoroquinolone.
  • Saltwater: doxycycline.
  • Animal bites: amoxicillin-clavulanate; alternatives if penicillin allergic.

Pediatric Considerations

  • Avoid doxycycline ≤8 years.
  • Use Melbourne ASSET tool to guide IV antibiotic need.

Surgery

  • Debridement for necrotizing infection or abscess.
  • Airway management for head/neck cellulitis if needed.

Admission Criteria

  • Severe systemic toxicity.
  • Rapid progression or necrosis.
  • Immunocompromised or comorbidities.
  • Failure of outpatient therapy.

Ongoing Care

  • Monitor clinical response and labs if indicated.
  • Expect symptom improvement in 24-48 hours; visible improvement in 72 hours.

Diet

  • Glycemic control in diabetic patients.

Patient Education

  • Skin hygiene, moisturizing to prevent barrier breakdown.

Prognosis

  • Worse with older age, higher BMI, diabetes.

Complications

  • Abscess formation.
  • Bacteremia/sepsis.
  • Superinfection.
  • Lymphangitis, thrombophlebitis.
  • Meningitis.
  • Gangrene.

Clinical Pearls

  • S. aureus and group A Streptococcus most common causes.
  • Consider MRSA if purulence or no response after 48 hours antibiotics.
  • Rapidly expanding cellulitis with severe pain may indicate necrotizing fasciitis—urgent surgery needed.
  • Venous stasis dermatitis often mimics cellulitis; differentiate to avoid unnecessary antibiotics.

References:

  1. Stevens DL, Bisno AL, Chambers HF, et al. Practice guidelines for diagnosis and management of skin and soft tissue infections: 2014 update. Clin Infect Dis. 2014;59(2):147-159.
  2. Clebak KT, Reedy-Cooper A, Partin MT, et al. A guide to the treatment of cellulitis and other soft-tissue infections. J Fam Pract. 2021;70(5):214-219.
  3. Bender S, Oakden K. New developments and treatment options of cellulitis in the hospital. Clin Approaches Hosp Med. 2018;77-87.