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Introduction
Cellulitis is a diffuse, spreading bacterial skin infection that involves the subcutaneous tissues. This typically occurs in areas where skin integrity has been compromised. This more commonly affects the lower extremities in adults, and the face and neck in children. Cellulitis may also result from blood-borne spread of infection to the skin and subcutaneous tissues.
Erysipelas is a type of cellulitis with sharply demarcated margins that involve the epidermis and superficial lymphatics. This is also referred to as St Anthony’s fire. The onset of symptoms is acute with accompanying systemic manifestations, whereas cellulitis has an indolent course.
Epidemiology
Cellulitis continues to place a substantial and rising strain on healthcare systems internationally. Cellulitis is most commonly observed in young children and adults older than 60 years. Among individuals aged 15 to 44 years, males have a higher incidence compared to females. Along with the rise in emergency department visits, hospital admissions due to SSTIs are also increased in the United States.
Etiology
Cellulitis Erysipelas_Disease Background 1Cellulitis is commonly caused by beta-hemolytic streptococci and Staphylococcus aureus. Infection due to streptococci is rapidly spreading because of streptokinase, while S aureus infection is localized. Consider Methicillin-resistant S aureus (MRSA) in patients with recurrent cellulitis that are refractory to treatment or exposed to a hospital or nursing facility. This can also be caused by Streptococcus pneumoniae, Haemophilus influenzae, Gram-negative bacilli and anaerobes. Erysipelas, on the other hand, is more commonly caused by beta-hemolytic streptococci.
Pathophysiology
The skin serves as the body’s primary defense against microbial invasion. It functions as a physical barrier. The skin’s low pH, sebaceous secretions, and fatty acids inhibit pathogen growth, and its normal bacterial flora further prevents colonization by harmful microorganisms. Bacterial infection of the skin and underlying soft tissues usually occurs when they are introduced through a break in the integrity of the skin barrier. The bacteria attach to host cells, penetrate tissues, and release toxins. These endotoxins and exotoxins attract immune cells and cause local tissue damage by triggering enzymatic reactions, cellular dysfunction, and cell rupture.
Risk Factors
Cellulitis Erysipelas_Disease Background 2The predisposing factors of cellulitis and erysipelas are obesity, diabetes mellitus (DM) (eg diabetic foot ulcers) and malignancy, immunosuppression, alcoholism, intravenous (IV drug) abuse, atopic dermatitis, previous cutaneous damage (eg animal bites, abrasions, wounds, etc), surgery, edema from venous insufficiency or lymphatic obstruction, and water and soil exposure.