Two microbiologic categories

1) Type 1 = Polymicrobial (anaerobes + aerobes); common organisms include Streptococcus, Bacteroides, Staphylococcus, Clostridium, Enterococcus, etc.

2) Type 2 = monomicrobial; usually caused by group A streptococcus

Risk Factors

Advanced age

Diabetes

Skin breach (surgical incision, penetrating trauma, insect bite, IV drug use)

Obesity

Peripheral vascular disease

HIV

Immunosuppression / neutropenia

Malignancy

Alcoholism

Pregnancy / child birth

Clinical features

Erythema without sharp margins; however, early infections have little overlying skin changes (thrombosis of capillary beds has not yet occurred)

Severe pain; however, as condition progresses, the affected area can become insensate

Crepitus

Fever

Skin bullae/necrosis/ecchymosis/edema

Infection can spread as fast as 1 inch/hour

*Most commonly involves extremities (lower > upper, especially in diabetics)*

Common lab findings

Leukocytosis

Elevated inflammatory markers (CRP +/- ESR)

Elevated CK and AST - suggest deep infection involving muscle/fascia

Elevated serum creatinine

Elevated serum lactate

Hyponatremia

Surgery is gold standard for treatment and diagnosis

Diagnosis is established via surgical exploration in OR; surgery should NOT be delayed for lab work/imaging if there is clinical suspicion

Imaging

Best radiographic imaging is CT scan with contrast

XRAY, US, MRI can also be used however not as helpful as CT

Treatment

Surgical debridement of necrotic tissue + Antibiotics

Antibiotics alone NOT effective

Antibiotics need to cover gram positives, gram negatives, and anaerobes

Sources

Tintinalli, JE. Tintinalli's Emergency Medicine: A Comprehensive Study Guide. 8th ed. New York, NY: McGraw-Hill Education LLC, 2016.

Wong, Chin-Ho, et al. "Necrotizing fasciitis: clinical presentation, microbiology, and determinants of mortality."JBJS85.8 (2003): 1454-1460.