Cellulitis is a common bacterial infection of the lower dermis and subcutaneous tissue. It results in a demarcated area of erythematous painful, swollen skin which are sometimes accompanied by systemic symptoms.
The most common causative agents are strep pyogenes (two thirds of cases) and staph aureus (one third). Rarer causes are pseudomonas aeruginosa usually in a puncture wound of the hand or foot, haemophilis influenza in children with facial cellulitis and pasteurella multocida due to cat or dog bite.
Cellulitis may lead to more serious complications such as necrotising fasciitis, gas gangrene and severe sepsis with multiorgan involvement.
Treatment should be as per your local antimicrobial guideline with the additional consideration of resuscitative treatment if more serious systemic involvement is suspected.