Cellulitis is a common bacterial infection of the skin that occurs because of a break in the skin barrier that allows organisms to invade. It leads to inflammation of connective tissue that is characterized by a reddening of skin with feeling of warmth and tenderness to the affected area. This can take place locally or, if serious, can affect the rest of the body and be potentially life threatening.
Generally, cellulitis is a condition that ensues in the extremities, but it can occur anywhere on the body. Risk factors include a disruption of the skin, blood vessel or lymphatic disorders, or a history of previous cellulitis. Breaks in the skin are commonly caused by trauma such as a cut, fungal infections of the feet that cause cracking and drying, or foot ulcers that frequently occur in diabetic patients. Disorders of the blood vessels or lymphatic system can occur in people who are overweight or pregnant. This can also occur in people with venous insufficiency, meaning one’s veins are not able to properly return blood back to the heart, causing pooling of blood. Because these conditions lead to less blood flow in the extremities, less cells of the immune system will be delivered by the blood to fight infection.
This infection is a clinical diagnosis, meaning it is diagnosed based on signs and symptoms of the patient and does not necessitate laboratory testing in most individuals. The hallmark local features around the injury are edema (swelling), erythema (redness), warmth, and tenderness. Also, the margins of redness usually are not demarcated. Without these classical features, it is strongly suggestive that the diagnosis is not cellulitis.
Commonly, this can affect the lymphatic system that is responsible for returning fluid to the blood. Lymph nodes around the area can be tender and enlarged, and lymphangitis can be evident (visible as red ascending streaks on the skin). Lymphangitis is strongly suggestive of cellulitis, but the absence of it does not rule out the diagnosis. The patient can also form an abscess (appearing as pus-filled cavity in an attempt by the body to wall off infection). If the infection affects the rest of the body or becomes systemic, patients can experience fevers, chills, fatigue, and myalgias (muscle aches); the illness can look similar to the common flu.
Usually, the bacterium that causes this infection is either Staphylococcus aureus or beta-hemolytic streptococci. Less commonly, other organisms can be involved in dog or cat bites, puncture wounds, or in an open wound exposure to fresh- or saltwater. It is appropriate to treat this empirically with antibiotics, meaning the patient is given an antibiotic that will treat the most common cause relating to their exposure. Blood or skin cultures are used only in those with systemic illness, recurrent cellulitis or risk factors for recurrent illness, atypical exposures, or for those who do not improve with treatment.
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