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A 4-year-old child presents with a fever and a red and swollen foot (Figure 126-1). The patient injured her foot 3 days ago by catching it in a door. On physical examination, the foot is warm, tender, red, and swollen, and the child's temperature is 39.4°C (103°F). The clinician diagnoses cellulitis and admits the child for IV antibiotics.

FIGURE 126-1

Cellulitis of the foot after an injury with a door in a 4-year-old girl. (Reproduced with permission from Richard P. Usatine, MD.)


Cellulitis is an acute infection of the skin that involves the dermis and subcutaneous tissues. Cellulitis causes erythema, swelling, warmth, and tenderness of the involved skin. Erysipelas is a specific type of superficial cellulitis with prominent lymphatic involvement leading to a sharply defined and elevated border (see Figure 126-6). Purulent cellulitis is defined as the presence of pustules, purulent drainage or an abscess within or adjacent to the cellulitis.


Cellulitis is a common skin infection, with more than 650,000 admissions per year in the United States alone.1,2

In the United States, an estimated 14.5 million cases annually of cellulitis account for $3.7 billion in ambulatory care costs.1,3


  • Cellulitis often begins with a break in the skin caused by trauma, excoriations, a bite, or an underlying skin disease (e.g., psoriasis, eczema, tinea pedis, stasis dermatitis) (Figures 126-2, 126-3, 126-4).

FIGURE 126-2

Cellulitis and abscess of the finger after a clenched fist injury in which the patient cut his finger on the tooth of the man he assaulted. (Reproduced with permission from Richard P. Usatine, MD.)

FIGURE 126-3

Cellulitis of the foot of a diabetic person in which there is possible necrosis and gangrene of the second toe, requiring hospitalization and a podiatry consult. (Reproduced with permission from Richard P. Usatine, MD.)

FIGURE 126-4

Cellulitis in an older man with venous stasis dermatitis. (Reproduced with permission from Richard P. Usatine, MD.)

The most common causative organisms are Streptococcus species and Staphylococcus aureus.1

Unfortunately, cellulitis is difficult to culture from the skin, so we have few reliable data about the organisms based on direct culture of the cellulitis. If there is coexisting purulence, S. aureus is likely to be involved.

Data from blood cultures can be used to help us understand the microbiology of the ...

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