Cellulitis - information

What is cellulitis? What are symptoms of cellulitis?

Cellulitis is a spreading bacterial infection of the skin and tissues beneath the skin. Cellulitis usually begins as a small area of tenderness, swelling, and redness. As this red area begins to enlarge, the person may develop a fever—sometimes with chills and sweats—and swollen lymph nodes ("swollen glands") near the area of infected skin.

Unlike impetigo, which is a very superficial skin infection, cellulitis refers to an infection also involving the skin's deeper layers: the dermis and subcutaneous tissue. The main bacteria involved in cellulitis are Staphylococcus ("staph"), the same bacteria that cause many cases of impetigo. Occasionally, other bacteria may cause cellulitis as well.

Where does cellulitis occur?

Cellulitis may occur anywhere on the body, but the leg is the most common site of the infection (particularly in the area of the tibia or shin bone and in the foot), followed by the arm, and then the head and neck areas. In special circumstances, such as following surgery or trauma wounds, cellulitis can develop in the abdomen or chest areas. In cases of morbid obesity, it can also develop in the abdominal area.

What does cellulitis look like?

The signs of cellulitis include redness, warmth, swelling, and pain in the involved tissues. Any skin wound or ulcer that exhibits these signs may be developing cellulitis.

Other forms of noninfected inflammation may mimic cellulitis. People with poor leg circulation, for instance, often develop scaly redness on the shins and ankles; this is called "stasis dermatitis" and is often mistaken for the bacterial infection of cellulitis.


What are risk factors for cellulitis?

Some cases of cellulitis appear in areas where the skin has broken open, such as the skin near ulcers or surgical wounds. Many times, however, cellulitis occurs where there has been no break in the skin at all, such as with chronic leg swelling (edema).

People who have diabetes or conditions that compromise the function of the immune system (for example, HIV/AIDS or those receiving chemotherapy or drugs that depress the immune system) are particularly prone to developing cellulitis.

Conditions that reduce the circulation of blood in the veins or that reduce circulation of the lymphatic fluid (such as venous insufficiency, obesity, pregnancy, or surgeries) also increase the risk of developing cellulitis.

What causes cellulitis?

The majority of cases of cellulitis are caused by either staph (Staphylococcus) or strep (Streptococcus) bacteria.

Staph (Staphylococcus aureus) is the most common bacteria that causes cellulitis. There is a growing incidence of community-acquired infections due to methicillin-resistant S. aureus (MRSA), a particularly dangerous form of this bacteria that is resistant to many antibiotics and is more difficult to treat.

Strep (usually group A or B Streptococcus) is also a common cause of cellulitis. A form of rather superficial cellulitis caused by strep is called erysipelas; it is characterized by spreading hot, bright red circumscribed area on the skin with a sharp raised border. The so-called "flesh-eating bacteria" are, in fact, also a strain of strep that can sometimes rapidly destroy tissues.

Cellulitis can be caused by many other types of bacteria. In children under 6 years of age, H. flu (Hemophilus influenzae) bacteria can cause cellulitis, especially on the face, arms, and upper torso. Cellulitis from a dog or cat bite or scratch may be caused by the Pasteurella multocida bacteria, which has a very short incubation period of only four to 24 hours. Aeromonas hydrophilia, Vibrio vulnificus, and other bacteria are causes of cellulitis that develops after exposure to freshwater or seawater. Pseudomonas aeruginosa is another type of bacteria that can cause cellulitis, typically after a puncture wound.

Is cellulitis contagious?

Cellulitis is not contagious because it is an infection of the skin's deeper layers (the dermis and subcutaneous tissue), and the skin's top layer (the epidermis) provides a cover over the infection. In this regard, cellulitis is different from impetigo, in which there is a very superficial skin infection that can be contagious.

How is cellulitis treated?

First, it is crucial for the doctor to distinguish whether or not the inflammation is due to an infection. The history and physical exam can provide clues in this regard, as can sometimes an elevated white blood cell count. A culture for bacteria may also be of value, but in many cases of cellulitis, the concentration of bacteria may be low and cultures fail to demonstrate the causative organism.

When it is difficult or impossible to distinguish whether or not the inflammation is due to an infection, doctors sometimes treat with antibiotics just to be sure. If the condition does not respond, it may need to be addressed by different methods dealing with types of inflammation that are not infected. For example, if the inflammation is thought to be due to an autoimmune disorder, treatment may be with a corticosteroid.

Antibiotics, such as derivatives of penicillin or other types of antibiotics that are effective against the responsible bacteria, are used to treat cellulitis. If the bacteria turn out to be resistant to the chosen antibiotics or in patients who are allergic to penicillin, other appropriate antibiotics can be substituted. In many cases, treatment requires the administration of intravenous antibiotics in a hospital setting, since oral antibiotics may not always provide sufficient penetration of the injury to be effective. In certain cases, intravenous antibiotics can be administered at home.

In all cases, physicians choose a treatment based upon many factors, including the location and extent of the infection, the type of bacteria causing the infection, and the overall health status of the patient.


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