Background

Skin and soft tissue infections are frequent reasons for visits to emergency departments (EDs); in the United States, approximately $3.7 billion of ambulatory care costs are expended on the estimated 14.5 million cases of cellulitis every year.¹ Nationally representative data from 2000 to 2015 demonstrated a rise in the incidence of outpatient visits for skin infections.²

The accurate diagnosis of cellulitis, erysipelas, and abscess is important – underdiagnosis can lead to infections progressing beyond their initial areas of presentation, and overdiagnosis can lead to unnecessary antibiotic use.^3–5 The risk of abscess formation increases with increasing prevalence of community‐acquired methicillin‐resistant Staphylococcus aureus strains.⁶ The incidence of skin and soft tissue infection is twice that of urinary tract infections and 10‐fold of that of pneumonia in patients aged 0–64 years. Among patients younger than 65 years, the incidence of skin infections is 49 cases/1000 person/year. Most skin and soft tissue infections (95%) are treated in the ED and ambulatory settings. Complications such as myositis, gangrene, and sepsis occurred in 0.9% and 16.9% of ambulatory‐treated and inpatient‐treated patients, respectively.⁶ Please refer to Chapter 25 for Necrotizing Fasciitis and Chapter 31 for Sepsis.

Nevertheless, the diagnosis can be a difficult one; a recent narrative review listed 33 different mimics of cellulitis that may present with similar findings.⁷ While antibiotic selection and the merits of various abscess drainage techniques are beyond the scope of this text, the two clinical questions below are relevant to almost every patient with potential cellulitis or abscess presenting to the ED.

Clinical question

Can history or physical exam accurately rule in or rule out cellulitis and abscess?

This question is fundamental to the diagnosis of skin and soft tissue infections. Cellulitis is typically described as a poorly demarcated area of erythema in a patient with fever, pain, warmth, and swelling, but these findings are all relatively insensitive and nonspecific.¹ A 2017 meta‐analysis by Quirke et al.⁸ included 6 studies and 2471 patients with nonpurulent leg cellulitis. From a total of 40 risk factors, several aspects of the history and physical exam increased the odds of developing cellulitis (Table 58.1). Local risk factors were found to be more significantly related to nonpurulent cellulitis compared to systemic risk factors. Previous cellulitis, previous leg surgery, having a wound, ulcer, excoriation, toe intertrigo, and chronic leg edema were the most common factors. The authors reported that patients with diabetes were more likely to present with suppurative cellulitis from infected diabetic foot ulcers or wounds and may have been excluded from the systematic review. Also, the articles had to specifically report cellulitis affecting the lower extremities to be included.