The Role of Bacterial Skin Infections in Atopic Dermatitis

Expert Statement and Review From the International Eczema Council Skin Infection Group

H. Alexander; A.S. Paller; C. Traidl-Hoffmann; L.A. Beck; A. De Benedetto; S. Dhar; G. Girolomoni; A.D. Irvine; P. Spuls; J. Su; J.P. Thyssen; C. Vestergaard; T. Werfel; A. Wollenberg; M. Deleuran; C. Flohr

Disclosures

The British Journal of Dermatology. 2020;182(6):1331-1342. 

In This Article

Abstract and Introduction

Abstract

Patients with atopic dermatitis (AD) have an increased risk of bacterial skin infections, which cause significant morbidity and, if untreated, may become systemic. Staphylococcus aureus colonizes the skin of most patients with AD and is the most common organism to cause infections. Overt bacterial infection is easily recognized by the appearance of weeping lesions, honey-coloured crusts and pustules. However, the wide variability in clinical presentation of bacterial infection in AD and the inherent features of AD – cutaneous erythema and warmth, oozing associated with oedema, and regional lymphadenopathy – overlap with those of infection, making clinical diagnosis challenging. Furthermore, some features may be masked because of anatomical site- and skin-type-specific features, and the high frequency of S. aureus colonization in AD makes positive skin swab culture of suspected infection unreliable as a diagnostic tool. The host mechanisms and microbial virulence factors that underlie S. aureus colonization and infection in AD are incompletely understood. The aim of this article is to present the latest evidence from animal and human studies, including recent microbiome research, to define the clinical features of bacterial infections in AD, and to summarize our current understanding of the host and bacterial factors that influence microbial colonization and virulence.

Introduction

Patients with atopic dermatitis (AD; also known as 'atopic eczema') have an increased risk of recurrent skin infections.[1–4] Staphylococcus aureus is the most common infectious organism, although beta-haemolytic streptococci may also be involved.[5–8]

The mechanisms underlying bacterial infection in AD are multifactorial and include both host and bacterial factors. The reduced skin barrier, cutaneous innate and adaptive immune abnormalities and trauma from scratching all contribute to the increased risk of skin infection.[9–13] The host skin microbiota may play a role in protecting against S. aureus colonization and infection in patients with AD.[14–17] Bacterial virulence factors, such as the superantigens, proteases and cytolytic phenol-soluble modulins (PSMs) secreted by S. aureus, cause skin inflammation and may also contribute to bacterial persistence and/or epithelial penetration and infection.[12,18,19]

The complex interaction between bacteria and host results in wide variability in the clinical presentation of infection in AD and can make the diagnosis challenging. Cutaneous infection may be associated with concomitant AD flares, and the classic signs of infection (erythema, oozing and crusting and increased cutaneous warmth) are masked by similar clinical features of AD itself. Increases in erythema in individuals with darker skin types are more difficult to appreciate, making diagnosis yet more challenging. Pustules are an uncommon sign of bacterial infection in AD, but if present they can allow the diagnosis to be made with greater certainty. Diagnosis and management decisions are further complicated by the fact that the main causative organism, S. aureus, commonly colonizes even nonlesional, clinically unaffected AD skin, thus limiting the usefulness of bacterial cultures in identifying the causative organism.

Untreated bacterial skin infection in AD may become systemic and lead to life-threatening complications including sepsis, endocarditis and bone and joint infections.[20–22] Despite the significant morbidity caused by bacterial skin infection in AD, there is a lack of consensus on how to define and treat associated bacterial colonization and infection. Although there are many diagnostic criteria for AD itself, there are no validated diagnostic criteria for infected AD.[23]

The International Eczema Council, a group of approximately 100 experts in AD worldwide, has recently initiated a taskforce to define the role of bacterial skin infections and their management in AD through consensus statements in an effort to provide level D evidence. It is hoped that input from clinical experts will contribute to better defining the wide-ranging clinical presentations of S. aureus infection in AD and, more importantly, to identify better those who may benefit from existing or novel antimicrobial treatments. Based on a systematic search of the literature, including terms for AD and 'infection', 'bacteria', 'staphylococcus aureus' and 'microbiome' (detailed search strategy available on request), this narrative review defines the clinical features of bacterial infection in AD and our current understanding of the host and bacterial factors that influence microbial colonization and virulence.

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