Necrotizing Soft Tissue Infections - Complicated Skin Infections

  • Diagnosis
  • Background
  • Lab Tests
  • References
  • Related Topics

Indications for Testing

  • Appropriate clinical presentation in addition to a high level of suspicion for the disease

Laboratory Testing

  • Simple infections – abscesses, furuncles, carbuncles
    • Gram stain of aspirates or tissue biopsies – may not be as helpful as culture, depending on organism involved and quality of specimen
    • Culture
      • Tissue
      • Wound
  • Complicated infections (fever, tachycardia, immunocompromised patients)
    • CBC
    • Culture
      • Tissue
      • Wound
      • Blood – infrequently positive
    • C-reactive protein
    • Laboratory Risk Indicator for Necrotizing Fasciitis (LRINEC) score – ≥6 points has positive predictive value of 92% and negative predictive value of 96% for diagnosis of necrotizing fasciitis
  • If above studies do not confirm necrotizing fasciitis, surgical exploration of the site may confirm the disease

Imaging Studies

  • X-ray – subcutaneous air in tissue noted in about 25% of patients with complicated infections
    • May reveal foreign body in infected wounds
  • US/CT/MRI – choose imaging study based on suspected location of infection and usefulness of study for site infected
    • Imaging frequently used for localized drainage of identified site

Differential Diagnosis

Aggressive soft tissue infections can cause extensive local tissue damage as well as systemic toxicity. These infections require prompt recognition in order to prevent severe morbidity and mortality.


  • Incidence – 4/100,000
  • Age – increased frequency in older patients
  • Sex – M:F, equal
    • Exception in Vibrio vulnificus, M>F
  • Transmission – skin entry via break in dermis


  • Gangrene
  • Necrotizing fasciitis/cellulitis
  • Myositis/myonecrosis
  • Complicated/deep abscesses
  • Infected burns/surgical wounds
  • Toxin-mediated – toxic shock syndrome, staphylococcal scalded skin syndrome


  • Organisms depend on type of infection
    • Uncomplicated infections – single organism most common
    • Complicated infections – polymicrobial more prominent
  • Common organisms
    • Staphylococcus spp (including methicillin-resistant Staphylococcus aureus[MRSA]), enterococci, Pseudomonas aeruginosa, Streptococcus spp, Enterobacteriaceae, Bacteroides spp, Proteus spp, Clostridium spp
    • Most common – Staphylococcus aureus, Streptococcus spp
    • Aerobic and anaerobic organisms frequently found in polymicrobial infections

Risk Factors

Clinical Presentation

  • General symptoms
    • Skin – erythema, tense edema, vesicles or bullae, necrosis ulcers, crepitus, gray or discolored wound drainage, pain extending past margin of skin infection
    • Constitutional – fever, diaphoresis, delirium, tachycardia, tachypnea
    • Most common locations – extremities (50-55%), perineum/buttocks (20%), trunk (18-20%), head and neck (8-10%)
  • Clinical markers that may help differentiate necrotizing infection from localized infection include the following
    • Pain disproportionate to appearance of infection
    • Crepitus
    • High fever
    • Rapidly spreading erythema


  • Initiate antibiotic therapy appropriate for polymicrobial infections; change therapy to match culture results
  • Aggressive wound care, including wide-area surgical debridement
    • Necrotizing wounds are commonly fatal if not treated within 72 hours


  • Vibrio – do not eat raw seafood; avoid exposing open wounds to seawater
  • Pasteurella – prophylaxis started at time of bite for serious bite wounds
Tests generally appear in the order most useful for common clinical situations. Click on number for test-specific information in the ARUP Laboratory Test Directory.

CBC with Platelet Count and Automated Differential 0040003
Method: Automated Cell Count/Differential


May not be elevated in spite of aggressive disease

Wound Culture and Gram Stain 0060132
Method: Stain/Culture/Identification


Anaerobe culture is NOT included with this order

Tissue Culture and Gram Stain 0060127
Method: Stain/Culture/Identification


Anaerobe culture is NOT included with this order

Blood Culture 0060102
Method: Continuous Monitoring Blood Culture/Identification


Testing is limited to the University of Utah Health Sciences Center only

C-Reactive Protein 0050180
Method: Quantitative Immunoturbidimetry

Electrolytes, Urine 0020498
Method: Quantitative Ion-Selective Electrode

Glucose, Plasma or Serum 0020024
Method: Quantitative Enzymatic


May AK. Skin and soft tissue infections: the new surgical infection society guidelines. Surg Infect (Larchmt). 2011; 12(3): 179-84. PubMed

Stevens DL, Bisno AL, Chambers HF, Dellinger P, Goldstein EJ, Gorbach SL, Hirschmann JV, Kaplan SL, Montoya JG, Wade JC. Practice guidelines for the diagnosis and management of skin and soft tissue infections: 2014 update by the infectious diseases society of America. Clin Infect Dis. 2014; 59(2): 147-59. PubMed

General References

Breen JO. Skin and soft tissue infections in immunocompetent patients. Am Fam Physician. 2010; 81(7): 893-9. PubMed

Edlich RF, Cross CL, Dahlstrom JJ, Long WB. Modern concepts of the diagnosis and treatment of necrotizing fasciitis. J Emerg Med. 2010; 39(2): 261-5. PubMed

Howell GM, Rosengart MR. Necrotizing soft tissue infections. Surg Infect (Larchmt). 2011; 12(3): 185-90. PubMed

Mullangi PK, Khardori NM. Necrotizing soft-tissue infections. Med Clin North Am. 2012; 96(6): 1193-202. PubMed

Napolitano LM. Severe soft tissue infections. Infect Dis Clin North Am. 2009; 23(3): 571-91. PubMed

Rajan S. Skin and soft-tissue infections: classifying and treating a spectrum. Cleve Clin J Med. 2012; 79(1): 57-66. PubMed

Ramakrishnan K, Salinas R, Agudelo Higuita N. Skin and Soft Tissue Infections. Am Fam Physician. 2015; 92(6): Online. PubMed

Turecki MB, Taljanovic MS, Stubbs AY, Graham AR, Holden DA, Hunter TB, Rogers LF. Imaging of musculoskeletal soft tissue infections. Skeletal Radiol. 2010; 39(10): 957-71. PubMed

Ustin JS, Malangoni MA. Necrotizing soft-tissue infections. Crit Care Med. 2011; 39(9): 2156-62. PubMed

Wilson ML, Winn W. Laboratory diagnosis of bone, joint, soft-tissue, and skin infections. Clin Infect Dis. 2008; 46(3): 453-7. PubMed

Wong C, Khin L, Heng K, Tan K, Low C. The LRINEC (Laboratory Risk Indicator for Necrotizing Fasciitis) score: a tool for distinguishing necrotizing fasciitis from other soft tissue infections. Crit Care Med. 2004; 32(7): 1535-41. PubMed

References from the ARUP Institute for Clinical and Experimental Pathology®

Chari A, Oakeson KF, Enomoto S, Jackson G, Fisher MA, Dale C. Phenotypic characterization of Sodalis praecaptivus sp. nov., a close non-insect-associated member of the Sodalis-allied lineage of insect endosymbionts Int J Syst Evol Microbiol. 2015; 65(Pt 5): 1400-5. PubMed

de Dios A, Jacob S, Tayal A, Fisher MA, Dingle TC, Hamula CL. First Report of Wohlfahrtiimonas chitiniclastica Isolation from a Patient with Cellulitis in the United States J Clin Microbiol. 2015; 53(12): 3942-4. PubMed

Medical Reviewers

Last Update: August 2017