Introduction
Cellulitis is an inflammation of the connective tissue underlying the skin that can be caused by bacterial infection. Cellulitis can be caused by normal skin flora or by exogenous bacteria, and often occurs where the skin has previously been broken: cracks in the skin, cuts, blisters, burns, insect bites, surgical wounds, or sites of intravenous catheter insertion. The mainstay of therapy remains treatment with appropriate antibiotics. Skin on the face or lower legs is most commonly affected by this infection, though cellulitis can occur on any part of the body. Cellulitis may be superficial — affecting only the surface of the skin — but cellulitis may also affect the tissues underlying the skin and can spread to the lymph nodes and bloodstream.
Cellulitis is unrelated to cellulite, a cosmetic condition featuring dimpling of the skin.
Symptoms
Early symptoms may include fever, headache, nausea, and early signs of redness on the affected area.
Cellulitis is characterized by redness, swelling, warmth, and pain or tenderness. Cellulitis frequently occurs on exposed areas of the body such as the arms, legs, and face. Other symptoms can include fever or chills and headaches. In advanced cases of cellulitis, red streaks (sometimes described as 'fingers') may be seen traveling up the affected area. The swelling can spread rapidly.
Causes
Cellulitis is caused by a type of bacteria entering by way of a break in the skin. This break need not be visible. Group A Streptococcus and Staphylococcus are the most common of these bacteria, which are part of the normal flora of the skin but cause no actual infection until the skin is broken. Predisposing conditions for cellulitis include insect bite, animal bite, tattoos, pruritic(搔癢症的) skin rash, recent surgery, athlete's foot, dry skin, eczema, injecting drugs (especially subcutaneous or intramuscular injection or where an attempted IV injection "misses" or blows the vein); plus burns and boils, though there is debate as to whether minor foot lesions contribute and also morbidly(不健全地,病態地) obese people can experience it.
The appearance of the skin will help a doctor make a diagnosis. The doctor may also suggest blood tests, a wound culture or other tests to help rule out a blood clot deep in the veins of the legs. Cellulitis in the lower leg is characterized by signs and symptoms that may be similar to those of a clot occurring deep in the veins, such as warmth, pain and swelling.
This reddened skin or rash may signal a deeper, more serious infection of the inner layers of skin. Once below the skin, the bacteria can spread rapidly, entering the lymph nodes and the bloodstream and spreading throughout the body.
In rare cases, the infection can spread to the deep layer of tissue called the fascial lining. Necrotizing fasciitis, also called by the media "flesh-eating bacteria", is an example of a deep-layer infection. It represents an extreme medical emergency.
Risk factors
The elderly and those with weakened immune systems are especially vulnerable to contracting cellulitis. Diabetics are more susceptible to cellulitis than the general population because of impairment of the immune system; they are especially prone to cellulitis in the feet because the disease causes impairment of blood circulation in the legs leading to foot ulcers. Poor control of blood glucose levels allows bacteria to grow more rapidly in the affected tissue and facilitates rapid progression if the infection enters the bloodstream. Neural degeneration in diabetes means these ulcers may not be painful and thus often become infected.
Immunosuppressive drugs, HIV, and other illnesses or infections that weaken the immune system are also factors that make infection more likely. In addition, chickenpox and shingles(帶狀皰疹) often result in blisters(水泡) which break, providing a gap in the skin through which bacteria can enter. Lymphedema, which causes swelling on the arms and/or legs, can also put an individual at risk.
Diseases that affect blood circulation in the legs and feet, such as chronic venous insufficiency and varicose veins, are also risk factors for cellulitis.
Cellulitis is also extremely prevalent(流行的) amongst dense populations sharing hygiene facilities and common living quarters. Military installations which require communal showers provide such an environment, as it is prevalent among many recruits going through boot camp.
Diagnosis
Cellulitis is most often a clinical diagnosis, and local cultures do not always identify the causative(成為原因的) organism. Blood cultures usually are positive only if the patient develops generalized sepsis. Conditions that may resemble cellulitis include deep vein thrombosis, which can be diagnosed with a compression leg ultrasound, and stasis dermatitis, which is inflammation of the skin from poor blood flow.
Duration
In many cases, cellulitis takes less than a week to disappear with antibiotic therapy. However, it can take months to resolve completely in more serious cases, and can result in severe debility(衰弱) or even death if untreated especially if the symptoms are caused in women. If it is not properly cured it may appear to improve but can resurface again even after months and years.
Treatment
Antibiotics — typically a combination of intravenous and oral antibiotics — are administered. Bed rest and elevation of affected limbs is also recommended. Often physicians suggest patients drink plenty of fluids as well.
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