Cellulitis is a spreading bacterial infection just below the skin surface.

The word "cellulitis" actually means "inflammation of the cells." Specifically, cellulitis refers to a bacterial infection of the tissue just below the skin surface. It is most commonly caused by Streptococcus pyogenes or Staphylococcus aureus. Skin is the first defense against invading bacteria and other microbes. An infection can occur when skin is damaged due to surgery, injury, or a burn and bacteria infects the wound.

Disease-causing bacteria release proteins called enzymes that cause tissue damage. The body's reaction to this damage is inflammation, which is characterized by pain, redness, heat, and swelling. An untreated infection may spread to the lymphatic system (acute lymphangitis), the lymph nodes (lymphadenitis),the bloodstream (bacteremia), or into deeper tissues. Cellulitis most oftenoccurs on the face, neck, and legs.

A very serious infection, called orbital cellulitis, occurs when bacteria enter and infect the tissues surrounding the eye. In 50-70% of all cases of orbital cellulitis, the infection spreads to the eye(s) from the sinuses or the upper respiratory tract (nose and throat). Twenty-five percent of orbital infections occur after surgery on the face. Other sources of orbital infection include a direct infection from an eye injury, from a dental or throat infection, and through the bloodstream.

Infection of the tissues surrounding the eye causes redness, swollen eyelids,severe pain, and causes the eye to bulge out. This serious infection can lead to a temporary loss of vision, blindness, brain abscesses, inflammation ofthe brain and spinal tissues (meningitis), and other complications. Before the discovery of antibiotics, orbital cellulitis caused blindness in 20% of patients and death in 17% of patients. Antibiotic treatment has significantly reduced the incidence of blindness and death.

Although other kinds of bacteria can cause cellulitis, it is most often caused by Streptococcus pyogenes (the bacteria which causes strep throat) and Staphylococcus aureus. Streptococcus pyogenes is the so-called "flesh-eating bacteria" and, in rare caes, can cause a dangerous, deep skin infection called necrotizing fasciitis. These bacteria can be spread through contact with a person who has strep throat or an infected sore. Orbital cellulitis may be caused by bacteria which cannot grow in the presence of oxygen(anaerobic bacteria). In children, Haemophilus influenzae type B frequently causes orbital cellulitis following a sinus infection.

Persons who are at a higher risk for cellulitis are those who have a severe underlying disease (such as cancer, diabetes, and kidney disease), are takingsteroid medications, have a reduced immune system (because of AIDS, organ transplant, etc.), have been burned, have insect bites, have reduced blood circulation to limbs, or have had a leg vein removed for coronary bypass surgery.In addition, chicken pox, human or animal bite wounds, skin wounds, and recent surgery can put a person at a higher risk for cellulitis.

The characteristic symptoms of cellulitis are redness, warmth, pain, and swelling. The infected area appears as a red patch that gets larger rapidly within the first 24 hours. A thick red line which progresses towards the heart mayappear indicating an infection of the lymph vessels (lymphangitis). Other symptoms which may occur include fever, chills, tiredness, muscle aches, and ageneral ill feeling. Some people also experience nausea, vomiting, stiff joints, and hair loss at the infection site.

The characteristic symptoms of orbital cellulitis are eye pain, redness, swelling, warmth, and tenderness. The eye may bulge out and it may be difficult or impossible to move. Temporary loss of vision, pus drainage from the eye, chills, fever, headaches, vomiting, and a general ill feeling may occur.

Laboratory tests called cultures may be done to determine which kind of bacteria is causing a cellulitis infection, but these tests are not alwayssuccessful. Cultures check the affected tissue and/or bloodstream for bacteria. In addition, a blood test may be done to count the number of white blood cells in the blood. High numbers of white blood cells suggest that the body istrying to fight a bacterial infection. Patients suspected of having orbitalcellulitis may have a computed tomography scan (CT) taken of their head.

A normally healthy person is usually not hospitalized for mild or moderate cellulitis. The condition can be treated with antibiotics such as penicillins (Bicillin, Wycillin, Pen Vee, V-Cillin), erythromycin (E-Mycin, Ery-Tab), cephalexin (Biocef, Keflex), cloxacillin (Tegopen), which cure over 90% of all cellulitis cases in 7-10 days. Other general treatment measures include elevation of the infected area, rest, and application of warm, moist compresses to the infected area. Medications such as acetaminophen (Tylenol) or ibuprofen (Motrin, Advil) may be taken to relieve pain, and aspirin can be taken to decrease fever.

Persons with serious disease and/or those who are taking immunosuppressive drugs may experience a more severe form of cellulitis which can be life threatening. Serious complications include blood poisoning (bacteria growing in theblood stream), meningitis (brain and spinal cord infection), tissue death (necrosis), and/or lymphangitis (infection of the lymph vessels). Severe cellulitis caused by Streptococcus pyogenes can lead to destructive and life-threatening necrotizing fasciitis.

Persons at high risk for severe cellulitis will probably be hospitalized fortreatment and monitoring. Antibiotics may be given intravenously to these patients. Complications such as deep infection, or bone or joint infections, might require surgical drainage. Extensive tissue destruction may require plastic surgery to repair. In cases of orbital cellulitis caused by a sinus infection, surgery may be required to drain the sinuses.

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