Cellulitis is a diffuse skin infection that involves the deep dermis and the subcutaneous fat tissues. Unlike erysipelas, which demonstrates superficial skin involvement with distinct margins, cellulitis is diffuse and spreading with no distinct demarcations. Although the inciting event typically is not discernable, predisposing factors include traumatic skin lesions, including puncture wounds, lacerations, surgical wounds, and burns; prior history of cellulitis; dermatophyte infections, such as tinea pedis; pressure ulcers; eczema; dermatitis; vascular insufficiency; lymphedema; presence of a foreign body; malnutrition; and immunosuppressive conditions, such as diabetes mellitus and cirrhosis [22,23]. Any cutaneous surface may be involved, but the most common site of infection is the lower extremity [24,25]. In immu-nocompetent hosts, the microorganisms most commonly implicated include Gram-positive cocci such as beta-hemolytic streptococci (particularly S pyogenes) and S aureus. In immunocompromised hosts, other microorganisms need to be included as potential pathogens. For example, Group B strepto-coccal-associated skin and soft tissue infections should be considered in adults who are pregnant, elderly, diabetic, cirrhotic, or have cancer [26,27]. A necrotic skin lesion with a hemorrhagic halo in a febrile neutropenic patient should include P aeruginosa in the microbiologic differential diagnosis. Likewise, Vibrio vulnificus infection should be considered in cir-rhotic patients who present with hemorrhagic bullous lesions and septic physiology, particularly if there is a recent history of warm brackish water exposure or consumption of undercooked shellfish, such as oysters, that derive from warmer waters .
Patients who have cellulitis typically present with erythematous, edema-tous tender skin lesions that are warm to palpation. Regional lymphadenop-athy and lymphangitis may be present. Systemic signs usually are more prominent in patients who have associated bacteremia. The differential diagnosis for cellulitis is broad and includes deep and superficial venous thromboses; gout; herpes zoster; angioedema; contact dermatitis; relapsing polychondritis; local reactions to chemicals, foreign bodies, and insect venom; and lymphedema, among others .
The diagnosis typically is determined clinically particularly when the cellulitis is considered uncomplicated (ie, lack of systemic signs, absence of immunocompromising conditions, and minimal skin surface area involved). A recent review of the available reported literature concluded that blood cultures do not assist diagnostics or therapeutics in immunocompetent adults who present with acute cellulitis . Based on one analysis of 553 patients with community-acquired cellulitis, blood cultures are recommended when there is acute onset of infection in the geriatric patient associated with significant leukocytosis and high-grade fever or immunocompromised hosts . Other possible diagnostic modalities for cellulitis include needle aspiration and skin biopsy, especially for patents who have strange exposures, refractory infections, or immunocompromising comorbidities. Unfortunately, cultures yield an organism in less than one third of samples obtained by needle aspiration or biopsy of infected tissue [32-37]. Swabbing ipsilateral tinea pedis-affected areas for bacterial culture may be helpful in identifying the microbiologic cause of cellulitis [38,39]. In general, imaging studies are not indicated in cellulitis unless a complicating factor (ie, foreign body, osteomyelitis, abscess, necrotizing fasciitis) or alternative diagnosis (ie, deep venous thrombosis) is being considered.
Treatment in most cases is directed against streptococci and S aureus. In the afebrile, immunocompetent patient who has a small area of involvement, oral antibiotic therapy consisting of dicloxacillin, cephalexin, clinda-mycin, or erythromycin can be considered if the community antibiotic-resistance profiles are favorable . In immunocompetent patients who are more severely ill, initial parenteral antibiotics that can be used include nafcillin, oxacillin, or cefazolin . The emergence of methicillin resistance in S aureus isolates from the community needs to be considered because these organisms are resistant to beta-lactam antibiotics, such as penicillins and cephalosporins. Agents such as trimethoprim-sulfamethoxazole, doxy-cycline or minocycline, clindamycin, linezolid, vancomycin, and daptomycin often are used to manage community-acquired MRSA skin infections. Immobilization and elevation of involved areas and treatment of underlying predisposing conditions is recommended. Surgical evaluation should be considered when the development of necrosis and gas is suspected or when there is no response to appropriate antibiotics.
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