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Pathophysiology

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  • Acute infection affecting epidermis, dermis, &/or subcutaneous tissue; bacteria introduced into skin through trauma, lacerations, abrasions, etc.
  • Microbiology: S. aureus (MSSA & CA-MRSA) & β-hemolytic streptococci
    • CA-MRSA emerged in past decade as prominent cause of infections (N Engl J Med 2005;352:1436; Ann Intern Med 2006;144:309); CA-MRSA susceptible to PO medications such as tetracyclines, clindamycin, trimethoprim/sulfamethoxazole (TMP-SMX), & linezolid (J Infect Dis 2006;193:1495)
    • Unusual bacteria associated w/specific exposures (ex: Vibrio w/saltwater injury, Aeromonas w/freshwater injury, etc.)

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Diagnosis & Evaluation

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  • Signs & symptoms: rapidly spreading areas of erythema, edema, tenderness, skin warmth, peau d'orange (orange peel) skin, malaise, & regional lymphadenopathy; systemic signs (fever, ↑ WBC, etc.) not always present, but associated w/more severe infection
  • Clinical presentation: impetigo (discrete, crusty lesions; typically in children), erysipelas (“fiery-red,” raised, tender plaque w/defined border), cellulitis (diffuse, erythematous w/ill-defined borders; deeper than erysipelas), abscess (pus within superficial skin layers; may extend deeper into muscle; consider ultrasound, CT, etc., with deep abscesses)
  • Microbiology culture: superficial wound cultures/swabs not helpful; culture pus (if present) for organism identification & susceptibility; important if patient nonresponsive
    • Skin aspiration positive in <5–40%; blood cultures positive <5%

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Clinical Pearl 29-1

Streptococcal infections more likely to be nonpurulent; staphylococcal, especially CA-MRSA, infections are more likely to present with purulence/abscesses (Clin Infect Dis 2011;52:1).

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Treatment & Follow-Up

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Nonpharmacological Treatment

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Incision & drainage (I&D) in all abscesses (addition of systemic antibiotics in uncomplicated abscesses (≤5cm) may not be necessary (Antimicrob Agents Chemo 2007;51:4044); elevation of affected limb—↑ edema resolution

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Pharmacological Treatment

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  • Impetigo: topical mupirocin preferred & equivalent to PO ABX—only add PO ABX if failure to respond to mupirocin
  • Erysipelas: cephalexin, dicloxacillin, clindamycin (if PCN allergy); β-hemolytic strep → ↑ macrolide resistance
  • Abscess: I&D; may add anti-MRSA therapy (doxy/minocycline, TMP-SMX, clindamycin)
  • Cellulitis: PCN G still DOC for suspected strep; if MSSA concern → dicloxacillin or cephalexin; if MRSA concern → vancomycin, doxy/minocycline + cephalexin, TMP-SMX + cephalexin, clindamycin, linezolid
    • Vancomycin: dose ∼30mg/kg/d w/ ↓ dose in renal failure; troughs typically not needed for cellulitis; may consider in elderly, renal failure/Δ'ing renal function, obesity; target trough >10mcg/mL
    • TMP-SMX: 10mg/kg/d (TMP) in divided doses (1 DS tab = 160mg TMP); ↓ efficacy in larger, undrained abscesses
    • TMP-SMX & doxy/minocycline do not cover all Strep spp.; add cephalexin or PCN
    • Clindamycin: covers CA-MRSA but ∼50% isolates w/inducible resistance (perform D-Test per micro lab)
    • Linezolid, daptomycin, telavancin, ceftaroline—more expensive w/no advantage in routine cellulitis; reserve for resistant cases or intolerance to conventional ABX

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Clinical Pearl 29-2

PO antibiotics adequate 1st line therapy for uncomplicated infections.

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Monitoring & Follow-Up

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  • Area of erythema typically ↑ prior to ↓ (↑ inflammation from bacterial lysis); may add steroids to speed resolution (Scand ...

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