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ID10 Infectious Diseases
Skin and Soft Tissue Infections
Toronto Notes 2019
Skin and Soft Tissue Infections
Cellulitis
Definition
• acuteinfectionoftheskinprincipallyinvolvingthedermisandsubcutaneoustissue
Etiology
• commoncausativeagents:β-hemolyticstreptococci(byfarthemostcommoncauseofnon-purulent cellulitis) and occasionally S. aureus or S. lugdunensis
• immunocompromisedpatientsorwaterexposure:mayalsoincludeGram-negativerodsandfungi
• bitewounds:considerskinof“bitee”andmouthof“biter”
• riskfactors
■ trauma with direct inoculation, recent surgery
■ peripheral vascular disease, lymphedema DM, cracked skin in feet/toes (tinea pedis)
Clinical Presentation
• pain,edema,erythemawithindistinctborders±regionallymphadenopathy,systemicsymptoms (fevers, chills, malaise)
• canleadtoascendinglymphangitis(visibleredstreakinginskinalonglymphaticsproximaltoareaof cellulitis)
Investigations
• CBCanddifferential,bloodC&Siffebrile • skinswabONLYifopenwoundwithpus
Treatment
• consult local guidelines for appropriate antibiotic therapy
• antibiotics:cephalexin(broadercoverageifriskfactorsforGram-negativerods)
• ifextensiveerythemaorsystemicsymptoms,considercefazolinIV
• ifMRSAissuspected,empiriccoverageforMRSAmaybeconsidered(seeASimplifiedLookatAntibiotics,
ID47)
• limbrestandelevationmayhelpreduceswelling
Necrotizing Fasciitis
Definition
• life-andlimb-threateninginfectionofthedeepfasciacharacterizedbyrapidspread
Etiology
• twomainforms
■ TypeI:polymicrobialinfection–aerobesandanaerobes(e.g.S.aureus,Bacteroides,Enterobacteriaceae) ■ TypeII:monomicrobialinfectionwithGAS,andlesscommonlyS.aureus
Clinical Presentation
• painoutofproportiontoclinicalfindingsandbeyondborderoferythema
• edema,±crepitus(subcutaneousgasfromanaerobes),±fever
• infectionspreadsrapidly
• patientsmayrapidlybecomeverysick(tachycardia,hypotension,lightheadedness) • latefindings
■ skin turns dusky blue and black (secondary to thrombosis and necrosis) ■ induration, formation of hemorrhagic bullae
Investigations
• clinical/surgicaldiagnosis–doNOTwaitforresultsofinvestigationsbeforebeginningtreatment • bloodandtissueC&S
• serumCK(elevatedCKusuallymeansmyonecrosis–alatesign)
• plainfilmx-ray(softtissuegasmaybevisualized)
• surgicalexplorationfordebridementofinfectedtissue
Treatment
• resuscitationwithIVfluids
• emergencysurgicaldebridementtoconfirmdiagnosisandremovenecrotictissue(mayrequire
amputation)
• IVantibiotics
■ unknownorganism:meropenemorpiperacillin/tazobactam+clindamycinIV±vancomycinif MRSA is considered
■ Type I (polymicrobial): piperacillin/tazobactam + clindamycin IV
■ Type II (monomicrobial): cefazolin (or cloxacillin) + clindamycin IV; with confirmed GAS
infection, penicillin G + clindamycin IV
■ with Type II, evaluate for streptococcal toxic shock syndrome and the need for IVIg