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  Most cases of cellulitis can be safely managed as outpatients with oral antibiotics, elevation, and recheck in 24-48 hours.

  
  
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  All abscesses require drainage. Most patients can be safely discharged without antibiotics, but do need a recheck in 48 hours.

  
  
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  Patients who are systemically ill or immune compromised require intravenous (IV) antibiotics, laboratory and imaging studies, and admission.

  
  
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  Patients with pain out of proportion to physical exam findings, crepitus, or rapidly spreading erythema may have a life-threatening necrotizing infection requiring aggressive work-up, broad-spectrum IV antibiotics, and immediate surgical consultation for operative debridement.

Soft tissue infections represent a common complaint in the emergency department (ED). The term “soft tissue infection” refers to an infection of the skin and underlying tissue. It is the emergency physician’s objective to distinguish superficial infections (cellulitis, erysipelas, or abscess) from deep infections. If deep infections, such as necrotizing fasciitis, are not emergently diagnosed, they can cause significant morbidity and mortality.

Cellulitis is a progressive bacterial infection of the dermis and subcutaneous fat that is associated with leukocytic infiltration and capillary dilation (seen as erythema). It is caused by bacterial invasion of the skin, most often by Staphylococcus aureus, β-hemolytic streptococcus, and gram-negative bacilli such as Haemophilus influenzae. Methicillin-resistant Staphylococcus aureus (MRSA) is quickly becoming a common infecting agent in many community-acquired cases of cellulitis and abscesses.

Erysipelas is a skin infection that involves the lymphatic drainage system. Primarily, it is caused by invasion of the skin by Staphylococcus pyogenes in areas with impaired lymphatic drainage. It is common in infants, children, and older adults. It is usually found on the lower extremities (70%) or face (20%). The characteristic presentation is painful erythematous raised lesions, which may look like an orange peel. Red streaking representing inflammation of the underlying lymphatics may also be present.

Abscesses are localized pyogenic infections that can occur in any part of the body. Approximately 2% of all adult visits to the ED are for the treatment of cutaneous abscesses. Bacteria that normally colonize the skin are often the cause, with S. aureus being the most common organism involved. Mixed infections (aerobes and anaerobes) usually occur in the perineal areas.

Necrotizing infections are life and limb-threatening infections that involve the skin, subcutaneous tissue, fascia, and muscle. They usually occur in the setting of skin trauma, surgical procedures, decubitus ulcers, and immune compromise. These deadly infections are caused by a mixture of aerobic and anaerobic bacteria in most cases. Commonly isolated bacteria include S. aureus, S. pyogenes (ie, “flesh-eating bacteria”), enterococci, and anaerobes such as Bacteroides and Clostridium perfringens (ie, “gas gangrene”).

History

Ask about the time course and presence of systemic symptoms. Rapidly progressive infections with systemic symptoms require aggressive care in the ED. Patients should be asked about trauma (including bites, scratches, and possible foreign bodies), as it is the most common risk factor for developing a soft tissue infection. Other risk factors include obesity, malnutrition, immune compromise, intravenous (IV) drug use, vascular or lymphatic insufficiency, surgical procedures, and decubitus ulcers. The past medical history can be relevant, as anything that depresses the immune system (eg, steroids, diabetes, immunosuppressive drugs, elderly) predisposes the patient to soft tissue infections and may mask the severity of illness. Also, the status of tetanus immunization and previous antibiotic allergies should be ascertained.

Physical Examination

Vitals signs provide rapid clues to the severity of infection. Tachycardia and hypotension may indicate sepsis. Fever is not reliable, as it occurs in <10% of patients with simple cellulitis or abscess.

The skin examination is crucial, and it is important to completely undress the patient to examine the involved body part. Assess the involved area for erythema, warmth, edema, and tenderness (Figure 36-1A). Lack of tenderness helps differentiate infections from other causes of skin erythema and warmth, such as venous stasis. Evidence of lymphatic spread in the form of red lines tracking proximally from the wound, called lymphangitis, further suggests an infectious etiology (Figure 36-1B). Focal areas of fluctuance and induration may indicate abscess formation.