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  • Common infection of the deep dermis and subcutaneous tissue most often caused by streptococcal and staphylococcal species, resulting in erythema, swelling, warmth, and pain of the affected site.

  • Unilateral lower-extremity involvement is typical and systemic symptoms are usually absent.

  • Important local risk factors include compromise of the skin barrier or underlying lymphovascular system.

  • Diagnosis is most often made clinically because of frequently equivocal or negative workups.

  • Treatment consists of antibiotics, but multiple recurrences may be observed.

  • Common variants:

    • Erysipelas: sharply demarcated, bright red, edematous plaques resulting from superficial lymphatic infiltration.

    • Purulent cellulitis: localized pustules or abscesses associated with cellulitis.

Cellulitis is a common infection of the deep dermis and subcutaneous tissue, most often caused by bacteria, that presents with the classic signs of inflammation as described by the Roman scholar Celsus in the first century CE: redness (rubor), swelling (tumor), heat (calor), and pain (dolor). Erysipelas is a variant of cellulitis that predominantly affects the superficial lymphatic vessels and surrounding tissue. Unlike the ill-defined plaques characterizing classic cellulitis, erysipelas demonstrates sharply marginated edematous plaques and is strikingly red in color. Diagnosis may be challenging and relies predominantly on clinical findings as laboratory, serologic, microbiologic, histopathologic, and imaging studies are often equivocal or negative. For these reasons, despite the high prevalence of these infections, misdiagnosis is common and may lead to both treatment-related morbidity and significant health care costs.


Most modern studies group classic cellulitis and erysipelas together under the simple term cellulitis when evaluating pathogenesis, risk factors, diagnosis, and treatment; this chapter follows that convention. Other cutaneous bacterial infections, including pyodermas (Chap. 150), toxin-mediated infections (Chap. 152), and necrotizing soft-tissue infections (Chap. 153) are considered separately.


Skin and soft-tissue infections have been described for thousands of years.1 In the preantibiotic era, cellulitis had a mortality rate of approximately 11% and only two-thirds of patients treated were cured with treatment.2 Early therapies in the antibiotic era, including ultraviolet light, penicillin, and sulfonamide, significantly reduced mortality, although study designs were comparatively simpler than modern clinical trials.2 In recent years, the emergence of community-acquired methicillin-resistant Staphylococcus aureus (MRSA), an increasingly common cause of cellulitis, has affected the epidemiology and treatment of this infection.


Cellulitis is common and has increased in prevalence: in 1997 there were 4.6 million ambulatory visits for cellulitis or abscess in the United States, and this increased to 9.6 million in 2005.3 The incidence rate increased from 17.3 to 32.5 per 1000 population during this time period, which parallels the rise of community-acquired MRSA.3,4 In the United States, rates appear to have stabilized, although they continue to rise in other economically developed nations.5,6 More ...

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