Cellulitis

Cellulitis is an infection of either the dermis or subcutaneous layer of the skin that commonly follows damage to the skin. Bacteria enter the skin through cracks, peeling, insect bites or stings, animal bites, human bites, injury, trauma, diabetic ulcers, or wounds from recent surgery. Skin disorders, such as eczema, psoriasis, ulcers, and fungal infections, also provide a portal of entry for bacteria. Once inside the dermis, the bacteria cause inflammation and infection.

Cellulitis can occur anywhere on the body, but the lower extremities are the most common site, especially the skin over the tibia and foot. It may also occur on the abdomen or chest following surgery or trauma and on the abdomen of those who are morbidly obese. Orbital cellulitis, an acute infection of the orbital tissue and eyelids, may also occur.

Cellulitis may be more severe in patients with chronic disorders, such as diabetes and human immunodeficiency virus, and in those who are immunosuppressed following chemotherapy or organ transplantation. If treated promptly, the prognosis is usually good. Left untreated, cellulitis can quickly become life-threatening.

Causes

Cellulitis can be caused by a variety of organisms, including bacteria and fungi; however, group A Streptococcus and Staphylococcus aureus are the most common causes. The most common pathogens in children include Haemophilus influenzae, Streptococcus pneumoniae, and S. aureus. Methicillin-resistant S. aureus (MRSA), once primarily a health care–associated pathogen, has also emerged as a common cause. The community-acquired strain of MRSA has a distinct susceptibility pattern and is more virulent that its nosocomial counterpart. Community-acquired MRSA skin and soft tissue infections were first seen in children, athletes involved in contact sports, and prisoners. In many areas of the country today, community-acquired MRSA has emerged as the primary S. aureus organism, even in patients without the previously identified risk factors. Community-acquired MRSA strains continue to be commonly seen in children and young adults, but they occur in all age groups.

Complications

Possible complications include sepsis, local abscess, progression to other tissue areas, tissue necrosis, thrombophlebitis, osteomyelitis, meningitis (if cellulitis involves the face), and lymphangitis. Complications of orbital cellulitis include cavernous sinus thrombosis, hearing loss, septicemia, meningitis, and optic nerve damage.

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