6th July 2023

Cellulitis

An acute bacterial infection of the dermis and subcutaneous tissue. Commonly caused by Streptococcus pyogenes followed by Staphylococcus aureus. Atypical organisms are summarised below:

Table 1: Atypical organisms in cellulitis

Factors that predispose to cellulitis include diabetes mellitus, lymphoedema, immunodeficiency, and conditions that compromise the skin barrier (e.g. tinea pedis, eczema).

Presentation is usually on the lower limbs and unilateral. The skin is hot, tender and erythematous with indistinct borders. Bullae and petechiae may also form. Systemic features of infection may also be present.

Left leg cellulitis

Image Source: Wikimedia Commons (2007). Cellulitis3, Licensed under a creative commons licence. Available for free at: https://commons.wikimedia.org/wiki/File:Cellulitis3.jpg (Accessed on: 14 March 2023).

Diagnosis is usually clinical but can be supported by blood tests (leukocytosis, elevated CRP) and wound MCS (if skin is broken). A blood culture is warranted if the patient is systemically unwell. General measures include marking the involved area, elevation, and simple analgesia. Patients with uncomplicated infection can be managed with oral antibiotics (e.g. flucloxacillin 500mg QDS). Systemically unwell patients require admission and intravenous antibiotics. Patients with at least 2 separate episodes of cellulitis in the previous 12 months can be trialled on prophylactic phenoxymethylpenicillin 250mg BD.