2 Skin and Soft Tissue Infection: Flashcards Preview

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Flashcards in 2 Skin and Soft Tissue Infection: Deck (17):

  • Streptococcal Skin Infection
  • Risk Factors

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  • Streptococcal Skin Infection
  • Etiology

Most commonly Beta hemolytic streptococci (A, B also known as Streptococcus agalactiae, C and G) and Staphylococcus aureus


  • Pasteurella multocida from 
  • Capnocytophaga canimorsus from 
  • Vibrio vulnificus from 
  • Aeromonas hydrophila from 
  • Pseudomonas aeruginosa from 
  • Erysipelothrix rhusiopathiae infection in 
  • Cryptococcus neoformans in

  • Pasteurella multocida from cat bites
  • Capnocytophaga canimorsus from dog bites
  • Vibrio vulnificus from salt water wounds
  • Aeromonas hydrophila from fresh water wounds
  • Pseudomonas aeruginosa from hot tubs, burns, neutropenic patients, chronic wet wounds/ulcers
  • Erysipelothrix rhusiopathiae infection in workers with domestic animals
  • Cryptococcus neoformans in immunocompromised hosts


  • Streptococcal Skin Infection
    • Differential diagnosis (6)

  1. Abscess.
    • May have erythema and pain.
    • Boggy or fluctuant.
    • Requires incision and drainage.
    • Purulence is more commonly associated with S. aureus
  2. Deeper infection than skin:
    • necrotizing fasciitis, myonecrosis. Patients severely ill (septic)
    • requires surgical debridement of dead tissue.
    • High mortality
  3. Bursitis over joints.
    • Also boggy and requires drainage if inflamed
  4. Deep venous thrombosis.
    • Warm, swollen, red lower limb.
    • If involves femoral veins can embolize to lungs
  5. Contact dermatitis.
    • Lesions pruritic but not painful, often shiny and weepy.
  6. Gout.
    • Erythema and pain over joint


Prognosis for cellulitis

  • Most patients recover without problems
  • Attention must be paid to underlying cause to decrease frequency of recurrence
    • Risk of recurrence in lower limb cellulitis as high as 30%
    • Treat tinea pedis
    • Control peripheral edema
    • Consider long term low dose antibiotic prophylaxis


Streptococcal Skin Infection - Treatment

  • Assess severity of illness and presence of systemic toxicity (fever, hypotension, confusion, underlying conditions) Admit for further investigations and IV therapy if present (see next slide regarding sepsis)
  • Non purulent cellulitis can be treated with oral antistaphylococcal/ streptococcal beta lactams (cephalexin, cloxacillin, nafcillin)
  • Purulent cellulitis should be cultured and therapy aimed at underlying risks including consideration of MRSA


Cardinal features of sepsis

  • vasodilation,
  • accumulation of white cells 
  • increased microvascular permeability

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Staphylococcal Skin - general

  • S. aureus causes a multitude of infections ranging from localized skin infection to invasive infection of bone, joint, heart, lung and internal organs.
  • Development of resistance to antibiotics particularly with emergence of MRSA is a problem. Vancomycin resistant S. aureus have been reported


Risk for MRSA increased in

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Laboratory features of Staphylococcus aureus

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SA toxins

  • Heat stabile toxin causing food poisoning
  • Toxic shock syndrome toxin‐1 (TSST‐1) causing toxic shock syndrome
  • Exfoliating toxin causing scalded skin syndrome in neonates


Community associated MRSA toxins (2)

  1. Panton‐Valentine Leukocidin
    • Causes leukocyte destruction and tissue necrosis
    • Carried on staphylococcal cassette chromosome mec (SCCmec) IV which also carries the altered penicillin binding protein 2a that is responsible for methicillin resistance
    • May be present in some MSSA strains
  2. Alpha hemolysin.
    1. Creates pores in some cells. Necessary for pneumonia in mice models


Staphylococcal Skin Investigations

  • Cultures are important especially with increase in MRSA and need for specific antibiotic therapy for this organism
  • Severely ill patients should have multiple blood cultures including at day 2 or 3 after admission to look for clearance
  • Bacteremias should never be ignored and should have echocardiography to rule out endocarditis
  • Disseminated infection can occur to any site and should be investigated in the presence of site specific symptoms


Staphylococcal Skin - Treatment

  • MSSA treated best with beta lactams effective against S. aureus
  • Vancomycin for MRSA effective at high levels 
  • Know local susceptibility patterns for use of macrolides and clindamycin in beta lactam allergic patients
  • Remove infected prosthetic material (joints, lines, valves etc.) to increase cure rates
  • Invasive disease requires high dose IV therapy


  • Nosocomial Infection
    • Definition nosocomial MRSA
    • Risk Factors for acquisition

  • Definition nosocomial MRSA
    • Infection that occurs after 48 hours admission
    • Infection that occurs in community up to 12 months after admission to hospital
  • Risk Factors for acquisition
    • Long hospital stay
    • Antimicrobial exposure
    • Dialysis
    • Diabetes
    • Recent hospitalization


MRSA treatment

  • Issues with Treatment. Bacterial resistance is key
    • Best drugs against S. aureus are beta lactams.
    • Ineffective against MRSA
      • Alternatives not as good (vancomycin, linezolid)
      • Kill more slowly or not bactericidal
      • More toxic
      • More expensive
      • Poorer clinical outcomes


MRSA - Management

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