Cellulitis

Minimum criteria for cellulitis:

• redness, and

• warmth, and

• swelling, and

• pain, and

• unilateral involvement.

- If purulence/abscess, see Skin Abscess.

Cellulitis includes:

• erysipelas – acute, superficial, nonnecrotizing infection of dermis/hypodermis typically caused by streptococci. Classically presents with well defined raised edge/erythematous plaque of sudden onset associated with pain, swelling and fever.

• cellulitis - acute, subacute or chronic nonnecrotizing infection of dermis/ hypodermis that extends into the subcutaneous/connective tissues with/without lymphadenopathy and/or abscess formation.

Investigations:

- Superficial skin cultures not recommended.

Exceptions:

• if subcutaneous abscess present: incision and drainage with culture recommended.

• if toe web intertrigo: culture of fissures may yield pathogen (β-hemolytic strep/S. aureus/MRSA) to help guide treatment. Also culture for dermatophytes and treat if positive as may be source of bacterial entry/recurrence.

- In moderate-severe cellulitis (extensive involvement, systemic symptoms), WBC and CRP recommended.

- Blood cultures recommended if septic, temp ≥ 38.5°C, chills/rigors, lymphangitis, elevated lactate, WBC > 15x10⁹/L, or immunocompromised.

Management:

• Elevation of affected limb essential:

  • lower extremity – elevate higher than hip joint

  • upper extremity – elevate higher than shoulder.

• Assess response to initial antibiotic therapy at 3 days.

NB: Increased redness/extension of cellulitis may occur after initiation of antibiotic therapy (due to release of toxins); NOT a reliable marker of clinical status if otherwise improving.

• In moderate-severe cellulitis (extensive involvement, systemic symptoms), a decrease in WBC and/or CRP are useful markers to assess clinical improvement.

• If no response to initial antibiotic therapy in 3 days, consider other diagnoses (see Differential Diagnosis in Adult section) and/or change the antibiotic regimen.