Cellulitis

These materials are intended for general clinical education and guidance. They are not a substitute for a clinician’s knowledge, skill or judgment in treating patients.

Note: This document does not apply to patients with necrotizing infections, diabetic foot infection, animal bites, water exposure or periorbital cellulitis.

Background

Skin and soft tissue infections are a heterogeneous group of infections that may involve multiple layers of integument. Management depends on both severity and infection presentation.

Severity

• Mild: Localized symptoms without fever or other systemic manifestations
• Moderate to severe: Systemic symptoms and/or signs but without tissue necrosis

Infection presentation

• Non-purulent: Erysipelas, cellulitis
• Purulent: Skin abscess, furuncle, carbuncle

Initial assessment

• A clinical diagnosis is typically sufficient; consider an ultrasound to rule out a deep tissue abscess
• If there are concerns about necrotizing cellulitis or fasciitis, consult Plastic Surgery and Infectious Diseases immediately
• Bilateral lower extremity cellulitis is extremely rare; consider an alternative diagnosis for local findings
• Non-infectious mimickers of soft tissue infections include stasis dermatitis, lymphedema, deep vein thrombosis, drug eruption, hematoma, insect bites and gout

Common pathogens

• Beta-hemolytic streptococci (S. pyogenes [GAS], S. agalactiae, S. dysgalactiae) — usually cause non-purulent infections
• Staphylococcus aureus (MSSA and MRSA) — main cause of purulent infections

Empiric therapy (first-line)

Mild, non-purulent infection (cellulitis, erysipelas)

• Cephalexin 500 mg PO q6h

OR

• Cefadroxil 500 mg PO q12h

*For patients more than 100 kg, consider Cephalexin or Cefadroxil 1 g per dose

Mild, purulent infection (abscess/furuncle/carbuncle)

• Perform incision and drainage
• Consider antimicrobials for a large abscess (> 2 cm), multiple abscesses, immunocompromised patients and/or surrounding cellulitis:
  • Doxycycline 100 mg PO q12h
    OR
  • TMP-SMX DS 1 tab PO q12h

Moderate to severe, non-purulent infection (cellulitis/erysipelas)

• Cefazolin 2 g IV q8h

Moderate to severe, purulent infection

• Vancomycin 15 mg/kg IV q12h (target trough 8–15)

Note: Early oral switch is usually appropriate once the patient is stable and improving.

Alternative for patients allergic to first-line empiric regimen

Mild, non-purulent infection

• Clindamycin 300 mg PO q6h

Mild, purulent infection

• Doxycycline 100 mg PO q12h

OR

• TMP-SMX DS 1 tab PO q12h

Moderate to severe, non-purulent or purulent infection

• Vancomycin 15 mg/kg IV q12h (target trough 8–15)

Duration

• Generally, no more than five to seven days
• Continue treatment until there is clinical improvement in fever and pain. Persistent edema and erythema do not indicate treatment failure and do not warrant continuing or escalating antibiotics

Clinical pearls

• Superficial skin swabs are not recommended
• Consider consultation with Infectious Diseases and evaluation for other potential causative pathogens (Enterobacterales, Pseudomonas aeruginosa, anaerobes) in the following scenarios:
  • The patient worsens or fails to improve after ~72h of first-line therapy
  • The patient has an immune deficiency
  • The infection is adjacent to chronic open wounds, necrotic wounds, or involves bite injuries
  • The infection is in the perineal or head and neck areas