Editing Necrotising fasciitis (section)

== '''Classification''' ==

** Type I (polymicrobial - both aerobic and anaerobic bacteria - Fournier's)
*** Usually seen in elderly or those with underlying illness (diabetes, vascular disease, pressure ulcer, episiotomy, haemorrhoid/fissure)
*** Usually presents with gas in tissue
*** Typically seen with an anaerobic species (Bacteroides, Clostridium, or Peptostreptococcus) in combination with ''Enterobacteriacaeae'' (E coli, Enterobacter, Klebsiella, Proteus) and one or more facultative anaerobic streptococci (although not commonly group A strep)
*** The facultative anaerobes lower the local oxygen tension, allowing anaerobic proliferation
*** The anaerobes produce toxins and inhibit host phagocytosis
*** Marked leukaemoid reactions with Clostridial infection
** Type II (monomicrobial)
*** Usually Group A strep (GAS) or Staph aureus
*** Can occur in any age group and without underlying comorbidities
*** Half have a clear portal of entry and half do not (theorised to be haematogenous translocation from the throat to a site of blunt trauma or muscle strain)
*** 'M protein' is an important virulence determinant of GAS - M versions 1 and 3 are associated with streptococcal toxic shock syndrome, where pyrogenic exotoxins are produced, increasing cytokine production and contributing to shock
*** Usually seen with CRP >200, modestly increased WCC with marked left shift, and AKI in the absence of hypotension
** Type III (water-borne bacteria)
*** Vibrio, Aeromonas
*** Cirrhosis and eating contaminated oysters are risk factors
** Type IV (Candida and other fungi)