Skin and Soft Tissue Infections

Question 1

Erysipelas

Answer 1

• Caused by group A streptococci or streptococcus pyogenes
• 70-80 of cases affect the lower extremeties, 20% affect the face
• Predisposing factors:
  
  • Lympoedema
  • Venous stasis
  • Obesity
  • Diabetes
  • EtOH
• Streptococcal bacteraemia occurs in approximately 5% of cases
• Clincal features of site
  
  • Painful
  • Bright red
  • Oedematour
  • Peau d’orange
• Rarely cultured from surface of skin

Question 2

Scarlet Fever

Answer 2

• Most commonly dure to S.pyogenes, rarely similar with S.aureus
• Scarlatiniform rash:
  
  • Fine, red, rough textured
  • Blanching
  • Begins on chest, armpits and behind ears
    
    • ==> Desquamation after 2-5 days
• Symptoms due to exotoxin production

Question 3

Staphylococcal Scalded Skin Syndrome

Answer 3

• Commonly seen in infancy/early childhood
• Production of a circulating epidermolytic toxin ==> intradermal cleavage at the granular layer and desquamation
• Onset over a few hours to days , recovery within 5-7 days
• Worse sites tend to be face, neck, axilla and groin
• Scald-like appearance ==> large flaccid bulla
• Perioral crusting typical
• Intraepidermal blistering
• Very painful
• Caused by phage group II, benzylpenicillin-resistant (coagulase positive) staphylococci
• Tx - abx and analgesia

Question 4

Toxic Shock Syndrome

Answer 4

• Toxic shock syndrome is an uncommon but severe acute illness with fever, widespread red rash accompanied by involvement of other body organs.
• Caused by the release of exotoxins from toxigenic strains of the bacteria Staphylococcus aureus and Streptococcus pyogenes
  
  • Most commonly S.aureus ==> producing toxic shock syndrome toxin-1 (TSST-1)
  • Alternatively staphylococcal enterotoxin B or C
    
    • ==> Massive amounts of cytokines (cell-mediator chemicals):
      
      • Fever
      • Rash
      • Low blood pressure
      • Tissue injury
      • Shock
• Tx - IV abx and supportive

Question 5

Cellulitis

Answer 5

• An acute spreading infection of the skin extending deeper than erysipelas and involves the subcutaneous tissues. Blood cultures positive in 2-4%.
• Most often caused by S. aureus and Group A Streptococci but other beta haemolytic Streptococci eg. Groups C and G are implicated.
• Consider predisposing factors – eg occupation for Erysipeloid (contact with meat/fish), immunocompromised, disasters/earthquakes/hurricanes
  
  • May mean organisms may be more diverse eg. Vibrio vulnificus, Enterobacteriaceae, Pasteurella multocida
• Treatment should include antibiotics active against the most common isolates. Eg. Flucloxacillin, Benzyl-penicillin
  
  • ​Remember MRSA
  • May need to be more broad spectrum for eg. diabetic foot.

Question 6

Subcutaneous Tissue Infections

Answer 6

• Rapidly progressive cellulitis with extensive necrosis of the subcutaneous tissues and overlying skin
  
  • Necrotising fasciitis Types I and II (Type I = polymicrobial, Type II = Streptococcus pyogenes
  • Gas gangrene and anaerobic cellulitis (Clostridial/non-Clostridial). Clostridial cellulitis does not involve the deep fascia vs gangrene
  • Progressive bacterial synergistic gangrene
  • Fournier’s Gangrene
  • Gangrenous cellulitis in immunocompromised patients
• Usually secondary to direct spread from an adjacent site or penetrating injury
• Occasionally secondary to bacteraemic spread eg. Pseudomonas aeruginosa in the immunocompromised

Question 7

Necrotising Fasciitis

Answer 7

• An uncommon severe infection involving the subcutaneous soft tissues, particularly the superficial and often deep fascia
• Usually an acute rapidly progressing process
• Risk factors
  
  • For Type I: pre-exisiting conditions such as IDDM, EOH, elderly, male
  • For Type II, IVDU

Question 8

Necrotising Fasciitis - Clinical Features

Answer 8

• An uncommon severe infection involving the subcutaneous soft tissues, particularly the superficial and often deep fascia
• Usually an acute rapidly progressing process.
• Risk factors
  
  • For Type I: pre-exisiting conditions such as IDDM, EOH, elderly, male
  • For Type II, IVDU
• Exquisitely tender in the early stages, erythematous and swollen, rapidly progressing to skin breakdown and bullae formation within 3-5 days
• Frank cutaneous gangrene, area becomes anaesthetic secondary to thrombosis of small blood vessels and destruction of superficial nerves
  
  • Anaesthesia is a worrying clue and may pre-date obvious skin changes.

Question 9

Necrotising Fasciitis - Diagnosis

Answer 9

• A swab may not be enough
• Aspiration of pus or fluid
• Biopsy of tissues
• Serology eg ASO (anti-streptolysin O) titres
• Culture and antibiotic sensitivities of organisms grown

Question 10

Necrotising Fasciitis - Treatment

Answer 10

• Surgical drainage of pus and debridement of dead tissue
  
  • ==> Extensive and often disfiguring surgery
• Antibiotics
  
  • Against staphylococci and streptococci
  • Against anaerobes
  • May need high doses
• High dose intravenous immunoglobulin (IVIG) - anecdotal benefit
• Clearance of Staphylococcal carriage
• Nutrition and supportive care
• Hygeine

Question 11

Necrotising Fasciitis - Antibiotic Regimens

Answer 11

• High dose benzyl-penicilin + flucloxacillin + metronidazole
• Cephalosporins + metronidazole
• Meropenem + vancomycin or imepenem + vancomycin
  
  • Addition of high dose clindamycin for Type II (Streptococcus pyogenes)

Question 12

Gas Gangrene

Answer 12

• Usually the result of trauma
• Contamination of wound with spores of Clostridia, usually Clostridium perfringens
• May also occur after bowel surgery
• Other organsism are also involved in a synergistic infection

Question 13

Gas Gangrene - Treatment

Answer 13

• Antibiotics depends on culture results
  
  • Until known broad spectrum antibiotics eg. benzyl-penicillin + gentamicin + metronidazole or piperacillin/tazobactam or meropenem
• Essential to include anaerobic cover
• Surgery
• Hyperbaric oxygen

Question 14

Anthrax

Answer 14

• Caused by Bacillus anthracis
• At risk groups:
  
  • Tanners
  • Wool workers
  • Vets
  • Farmers
• ​Forms:
  
  • Cutaneous anthrax = malignant pustule
  • Pulmonary anthrax = due to inhalation of spores – high mortality
• Treatment = penicillin