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Bacterial skin infections

Acknowledgements

Developed in collaboration with the University of Auckland Goodfellow Unit in 2007.

Images have been sourced from the following:

  • Hon Assoc Prof Amanda Oakley
  • The Department of Dermatology, Health Waikato
  • Prof Raimo Suhonen (Finland)
  • Arthur Ellis (medical artist)

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Necrotising fasciitis

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Learning objectives

  • Recognise necrotising fasciitis

Clinical features

Necrotising fasciitis (NF) is infection of the subcutis and deep fascia. It is a surgical emergency, most often due to Streptococcus pyogenes producing pyrogenic exotoxins A, B and C (flesh-eating bacteria, Type 2 NF). It is less frequently polymicrobial (Type 1 NF) or due to Staphylococcus aureus, clostridia (gas gangrene, Type 3 NF) and other organisms.

  • NF may follow a surgical procedure or arise in apparently healthy individuals
  • It causes severe local pain and systemic toxicity
  • The surface may appear normal even when underlying tissue is widely necrotic
  • More often there is rapidly advancing erythema, painless ulcers and black necrotic eschar
  • Crepitus may occur in clostridial and other anaerobic infections
  • Anaerobes result in a foul smell
  • Associated with neutrophil leukocytosis, acute renal compromise, acidosis, coagulopathy and hyponatraemia

Investigations

The exudate should be gram stained. Rapid streptococcal diagnostic kit and polymerase chain reaction tests may be helpful for diagnosis. MRI or CT scans can be used to delineate the extent of NF.

Management

Management should include:

  • Admission to an intensive care unit.
  • Broad-spectrum antibiotics – these should be administered immediately, the choice depending on hospital policy (seek the advice of a medical microbiologist).
  • Debridement of necrotic tissue thoroughly and immediately by an experienced surgeon as a life-saving procedure. Excision of necrotic tissue may need to be repeated.

Intravenous immunoglobulins may be useful.

Some strains of Streptococci are more pathogenic due to certain extracellular products, toxins and superantigens. These may include cell surface molecules such as the M protein, opacity factor, the hyaluronic acid capsule, C5a peptidase and streptococcal inhibitor of complement (SIC), in addition to secreted proteins, pyrogenic and erythrogenic toxins, exotoxins, cysteine proteinase, streptolysins O and S, hyaluronidase, streptokinase and other enzymes.

Activity

Find out why non-steroidal anti-inflammatory drugs are contraindicated in the management of necrotising fasciitis.

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