Necrotizing fasciitis

Type I necrotizing fasciitis is a polymicrobial infection of subcutaneous tissue with anaerobes such as Bacteroides, Clostridium, or Peptostreptococcus and facultative anaerobes such as certain Enterobacterales (Escherichia coli, Enterobacter, Klebsiella, Proteus) or non-group A streptococcus with or without Staphylococcus aureus.[1]

Type II necrotizing fasciitis is a monomicrobial infection of subcutaneous tissue most commonly caused by Streptococcus pyogenes (group A streptococci) and occasionally Staphylococcus aureus. Panton-Valentine leukocidin (PVL)-positive Staphylococcus aureus,and MRSA are also potentially causative organisms.[1][2]

Other infectious etiologies may rarely cause a monomicrobial necrotizing infection associated with specific exposures or risk factors:

Aeromonas hydrophila, associated with freshwater exposure[3][9][10]
Vibrio vulnificus, from saltwater exposure or consumption of contaminated raw oysters[3][9][10]
Klebsiella pneumoniae, in South East Asian countries, in particular Taiwan[11]
Clostridium, can cause gangrenous necrotizing fasciitis (see Gangrene).
Pseudomonas aeruginosa, Enterobacterales, or Clostridium septicum in neutropenic children.[21]

Very rarely necrotizing fasciitis is a monomicrobial infection caused by fungal pathogens such as mucormycosis.[4] Mucormycosis has been reported as a cause in immunocompromised and immunocompetent patients.[12][13][14] Few cases of candida necrotizing fasciitis have been reported following surgery.[24]

Predisposing risk factors may include diabetes mellitus, peripheral vascular disease, immunocompromising conditions, chronic renal or hepatic insufficiency, chickenpox or herpes zoster, intravenous drug use, trauma or surgery, or certain medications (e.g., corticosteroids).[1][16][25][26]

Bacteria are introduced into the skin and soft tissue from minor trauma, puncture wounds, or surgery. However, in up to 20% of cases no primary site of infection is identified. Infection extends through the fascia but not into the underlying muscle, and tracks along fascial planes extending beyond the area of overlying cellulitis. Systemic signs of necrotizing fasciitis, such as fever, tachycardia, and hypotension, are primarily due to the action of bacterial toxins.[27][28]

Clinical presentation

Necrotizing fasciitis can be classified according to clinical presentation, which is based on clinical signs and symptoms, and their speed of onset.

Fulminant

This is the most severe type of necrotizing fasciitis and has a poor prognosis.[7] The patient will have extensive tissue necrosis that progresses over hours and will be systemically unwell with sepsis.[7]

Acute

Symptoms and signs develop over days. Typically associated with an identifiable skin or history of trauma, with pain out of proportion to the clinical findings.[7] The patient may initially be systemically well, but can deteriorate over days to hours.[7]

Insidious

Nonspecific or variable symptoms with an insidious onset.[7] Localized pain at the site of the skin lesion may be mild or absent.[7]

Causative organism

Necrotizing fasciitis can be classified according to the causative organism, once this is identified from blood or tissue cultures.

Type I

Polymicrobial infection with an anaerobe such as Bacteroides or Peptostreptococcus plus a facultative anaerobe such as certain Enterobacterales (Escherichia coli, Enterobacter, Klebsiella, Proteus) or non-group A streptococcus.[1][2][3][4] It is most commonly seen in older patients and in those with underlying illnesses.[8]

Type II

Monomicrobial infection, most commonly with Streptococcus pyogenes (group A streptococci), anaerobic streptococci, or rarely other pathogens such as Panton-Valentine leukocidin (PVL)-positive Staphylococcus aureus and MRSA.[1][2][3][4] Other infectious etiologies may rarely cause a monomicrobial necrotizing infection associated with specific exposures or risk factors:

Aeromonas hydrophila, associated with freshwater exposure.[3][9][10]
Vibrio vulnificus, from saltwater exposure or consumption of contaminated raw oysters.[3][9][10]
Klebsiella pneumoniae, in South East Asian countries, in particular Taiwan.[11]
Clostridium, can cause gangrenous necrotizing fasciitis. Usually follows severe penetrating trauma or crush injury with interruption of blood supply to the affected area. Can be difficult to differentiate clinically.[5] See Gangrene.

Very rarely monomicrobial infection is caused by fungal pathogens such as mucormycosis.[4] Mucormycosis has been reported as a cause in immunocompromised and immunocompetent patients.[12][13][14]

The classification above is based on the World Society of Emergency Surgery (WSES) global clinical pathways for patients with skin and soft tissue infections, and on expert opinion.[3] Some references, including other publications from WSES, further subclassify monomicrobial gram-negative infections including Aeromonas and Vibrio infections as type III and fungal infections as type IV.[2][15]

Anatomical location

Fournier gangrene is type I necrotizing fasciitis of the scrotum or male perineum.[1][2][3][4][5][16]

Meleney synergistic gangrene is gangrene of the tissues of the abdominal wall, with synergistic infection with Enterobacteria and Streptococcus.[17]

Cervicofacial necrotizing fascitis is a rapidly progressing gangrenous infection of the skin, subcutaneous tissue, and fascia of the neck and face.[18]

Further classifications exist and are sometimes used when discussing necrotizing fasciitis in the context of surgical site infections or rare organisms.

Pathophysiology