inpatient / infectious disease

Cellulitis / Skin and Soft Tissue Infection (SSTI)

Last Updated: 2/12/2023

# Cellulitis of *** with/without *** Purulence or c/f Abscess

-- ABCs: 
is the patient septic or unstable requiring the ICU?
-- Chart Check: prior infections, abx use, IVDU, immunosuppression
-- Admission Criteria: failed outpatient PO treatment, systemic symptoms, concern for necrotizing infection
-- HPI Intake: date started, focal and systemic symptoms, purulence, risk factors
-- Can't Miss: gas gangrene or necrotizing fasciitis, septic joint, DVT
-- Admission Orders: CBC, BMP, LFTs, BCx if systemic signs, consider US to check for abscess or DVT
-- Initial Treatment to Consider: PO vs IV antibiotics (cefazolin if not c/f MRSA, otherwise vanc); take pictures and draw margin lines to track progress

-- Date Started:
-- Focal Symptoms:
*** pain, erythema, warmth, tenderness, edema, c/f abscess
-- Systemic Symptoms:
*** fevers, chills, sweats, AMS
-- Purulence:
-- Insect or Animal Bites: ***
-- General RF’s:
*** trauma, stasis, edema, DM, radiation, IVDU, immunosuppressed
-- MRSA RF’s:
*** previous infection, hospital encounter in last 8 weeks, IVDU, penetrating trauma, dialysis, HIV, athlete, prisoner, military, long-term care facility
-- PsA RFs:
*** neutropenic, trauma, post-op

-- History: *** prior infections and abx use, IVDU, immunosuppression, timing,
-- Clinical: *** systemic symptoms,
-- Exam: *** erythema, warmth, tenderness, edema, poorly vs well demarcated, purulence, lymphadenopathy, necrosis or crepitus, pain out of proportion to exam, neuro exam if in limb (strength, sensation)
-- Data: *** WBC, wound culture, US
-- Etiology/DDx: *** septic joint, nec fasc, DVT, gout, contact dermatitis, stasis dermatitis, erysipelas superficial thrombophlebitis, angioedema, bursitis, erythema nodosum, pyoderma gangrenosum, sarcoid, GVHD, calciphylaxis, zoster, erythema migrans

The patient's HPI is notable for ***. Exam showed ***. Labwork and data were notable for ***. Taken together, the patient's presentation is most concerning for ***, with a differential including ***.

-- f/u CBC, BMP, LFTs
-- BCx if systemic signs or symptoms of infection or immunocompromise
-- consider US to evaluate for underlying abscess
-- I+D - send Cx if systemic symptoms or risk factors
-- CT if c/f nec fasc, pyomyositis, or osteomyelitis

-- Abx: *** (Strep: cefazolin 2g q8 or ceftriaxone 2g daily; MSSA: cefazolin or nafcillin 2g daily; MRSA: vancomycin, linezolid; if c/f nec fasc - add zosyn or cefepime + clinda); usually 5-14 days depending on severity, size, location
-- Narrowing: if no purulence, Keflex 500mg q6 or clindamycin 300-450mg q6-8 if PCN allergy; if purulence/abscess - can usually narrow to bactrim DS q12 or doxy 100mg q12 on discharge
-- Pain:
-- Supportive: rest, can trial ice packs, elevate affected extremity

If You Remember Nothing Else

Cellulitis and SSTI are most commonly caused by staph and strep. They are usually treated in the outpatient setting, but reasons for admission include failed outpatient PO treatment, systemic symptoms, or immunocompromised state. If it's a purulent infection, it is more likely MRSA. If the patient has bilateral disease, you should strongly consider other diagnoses such as stasis dermatitis. You can't miss gas gangrene or necrotizing fasciitis which requires immediate surgical attention as well as vanc/zosyn and clindamycin.

Clinical Pearls

  • Skin and Soft Tissue Infections (SSTIs) are infections of the epidermis, dermis, subQ tissue, or superficial fascia
  • Cellulitis is the acute spread of infection along the dermis and subQ tissue
  • The diagnosis of cellulitis is largely clinical
  • Staph and Strep (Group A) are the most common pathogens due to infiltration of the skin after disruption of the skin barriers (cuts, bites, etc)
  • Purulent infections are more likely staph and MRSA > MSSA; Non-purulent is mostly strep
  • MRSA Risk Factors: previous infection, hospital encounter in the last 8 weeks, IVDU, penetrating trauma, dialysis, HIV, athlete, prisoner, military, long-term care facility
  • Treatment options are based on the presence or abscence of purulence and the severity of disease
  • If bilateral, you should strongly consider other diagnoses
  • BCx and wound cultures have low yields and are not routinely obtained unless systemic symptoms, immunosuppression, bites, recurrent disease
  • Erythema may worsen initially when you start abx but should improve within 72 hours
  • Associations: Gas gangrene is associated with C perfringens; Dog/Cat bites associated with Pasteurella, capnocytophaga; Human bites associated with eikenella, oral anaerobes; Freshwater exposure is associated with Aeromonas, plesiomonas; Saltwater associated with Vibrio vulnificus; Neutropenia - PsA; Immunocompromised - fungal, Nocardia

Trials and Literature

  • EMERGEncy ID Net Study - MRSA was the most common identifiable cause of SSTI among patients presenting to the ED in 11 U.S cities, 95% of which are susceptible to clinda, 100% to bactrim, 92% to tetracycline (NEJM, 2006)

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