Skin and soft tissue infections

The skin acts as a barrier between the host and the environment. It comprises several layers and is colonized by various micro-organisms that may invade and cause infection of one or more layers. The most common pathogens are Staphylococcus aureus and group A streptococci. Infections of the skin and soft tissues are common and affect all age groups. Predisposing factors include pre-existing skin conditions, trauma, diabetes mellitus and immune suppression. They may occur as single or recurrent episodes, and may be mild and self-limiting or severe and progressive, leading to systemic complications such as bacteraemia and metastatic infection. Diagnosis is usually clinical, but investigations such as needle aspiration, biopsy or surgical debridement may sometimes be necessary to obtain specimens for microbiological examination and culture. This contribution discusses some common skin and soft tissue infections. Impetigo is a superficial infection of the epidermis. Deeper infections involving the dermis include ecthyma, folliculitis, furuncles, carbuncles, erysipelas and cellulitis. Wound infections are less common since the introduction of perioperative antibiotic prophylaxis. Their management varies according to the depth of infection. Bite infections are usually caused by domestic pets and most commonly affect the extremities; secondary antibiotic prophylaxis has been shown to be effective. Necrotizing fasciitis and gas gangrene are rare, severe infections that require prompt recognition, surgical debridement, appropriate antibiotic therapy and, often, intensive care support. Some uncommon causes of skin and soft tissue infections are also discussed.