- 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.)
- 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%
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).
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
- 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
- Area of erythema typically ↑ prior to ↓ (↑ inflammation from bacterial lysis); may add ...