Snapshot A 12-year-old boy presents to the emergency room for a red, hot finger. He had suffered from a papercut a few days ago. On physical exam, his left middle finger is red, swollen, tender, and hot to the touch. The edges are not well-demarcated, but borders are drawn anyway to track the progress of the erythema. Blood cultures are negative. He is started on penicillin for suspected cellulitis. Introduction Clinical definition painful bacterial infection involving the deeper dermis and subcutaneous tissues often from Streptococcal spp. or, less commonly, S. aureus from superficial involvement of skin to deep impetigo (very superficial skin infection) erysipelas (upper dermis and cutaneous lymphatics) cellulitis (deeper dermis and subcutaneous tissues) Epidemiology incidence 48 per 1000 person-years risk factors skin ulcers tinea pedis intravenous drug use venous insufficiency diabetes lymphedema pre-existing skin injury Etiology Streptococcus spp. S. aureus Pathogenesis pre-existing injury in skin can act as entry portal for bacteria Prognosis recurrence Presentation Symptoms painful and tense skin Physical exam fever diffuse inflammation of affected area poorly demarcated red warm tender dimpling around hair follicles resembling orange peel (peau d’orange) Studies Labs blood cultures Diagnosed clinically Differential Erysipelas more superficial involvement of skin and soft tissues there is often an overlap and may not be distinguished clinically from erysipelas Lymphedema asymptomatic non-pitting edema of the extremities best treated initially with conservative measures such as compression stockings Treatment Medical oral antibiotics indications for mild cases of cellulitis drugs penicillin dicloxacllin cephalexin clindamycin for suspected methicillin-resistant S. aureus IV antibiotics indications for cellulitis with signs of systemic infection e.g., positive blood cultures drugs penicillin cefazolin ceftriaxone clindamycin Complications Sepsis