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Cellulitis in Adult

See also in: Cellulitis DDx,Anogenital,Hair and Scalp,Oral Mucosal Lesion
Contributors: Sabrina Nurmohamed MD, Susan Burgin MD
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Cellulitis is a common bacterial infection of the deep dermis and subcutaneous tissue characterized by erythema, pain, warmth, and swelling. Pathogens of cellulitis are strongly correlated with age and immune status:
  • Immunocompetent adults: Staphylococcus aureus and Streptococcus pyogenes. Staphylococcus aureus is the most frequent etiology in children and in purulent cellulitis.
  • Immunocompromised individuals, including those with diabetes and decubitus ulcers: mixture of gram-positive cocci and gram-negative aerobes and anaerobes.
A focused history should determine immune status, comorbid conditions, possible sites and causes of skin barrier disruption, prior history of cellulitis, and methicillin-resistant S. aureus (MRSA) risk factors. The most common route of bacterial seeding in immunocompetent individuals is via direct inoculation, and in immunocompromised individuals, it is via hematogenous seeding. Risk factors include minor skin trauma, body piercing, intravenous drug use, tinea pedis infection, animal bites, peripheral vascular disease, immune suppression (chronic systemic steroid use, neutropenia, immunosuppressive medications, alcohol use disorder), and lymphatic damage (lymph node dissection, radiation therapy, vein harvest for coronary artery bypass surgery, and damage that occurs following multiple prior episodes of cellulitis). Implantable cardiac devices can also cause infection.

Fevers, chills, and malaise often precede the onset of cellulitis. Poorly defined borders, erythema, swelling, tenderness, and warmth characterize typical cellulitis lesions. In adults, the extremities are the most common sites affected. In more severe cases, additional clinical features may include vesicle and bulla formation, pustules, and necrosis. Complications are not common but can include glomerulonephritis, lymphadenitis, and subacute bacterial endocarditis.

A rising prevalence of MRSA has been identified as a pathogen of skin and soft tissue infections in otherwise healthy individuals lacking the aforementioned risk factors for cellulitis. MRSA should be considered for penetrating traumas, purulent infections, and in specific populations: athletes, children, prisoners, military service members, long-term care residents, and intravenous drug users. Other MRSA risk factors include recent admission to a health care facility, presence of an indwelling catheter, poor personal hygiene, and history of MRSA.

Note: Cellulitis virtually never occurs bilaterally at the same time. If redness and involvement of the legs are bilateral in a patient suspected to have cellulitis, consider an alternative diagnosis such as stasis dermatitis or contact dermatitis.

Related topics: Orbital Cellulitis, Preseptal Cellulitis


L03.90 – Cellulitis, unspecified

128045006 – Cellulitis

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Differential Diagnosis & Pitfalls

Cellulitis can be caused by many different bacterial pathogens, but the diagnosis is almost always made clinically. If a patient has had more than 1 episode of cellulitis, investigate risk factors for recurring cellulitis but also consider alternative diagnoses.

Stasis dermatitis is a frequent cause of bilateral leg redness. There are usually no systemic signs or leukocytosis; commonly it is bilateral with pruritus and red-brown dyspigmentation.

The differential for cellulitis is vast, and time course, drug / exposure history, and the presence / absence of systemic features should help delineate the cause. Below are common differential diagnoses:

Deep tissue infection

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Last Reviewed:12/06/2016
Last Updated:05/20/2019
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