Soft tissue infection: a normal white cell count and serum sodium make necrotising fasciitis less likely

Clinical bottom line (level 4)

  1. One in twelve patients admitted to hospital with a soft tissue infection have necrotising fasciitis.
  2. Patients with at least one 'hard' sign of necrotising fasciitis (hypotension, bullae, necrotic skin, gas on X-ray) are more likely to have it (LR + 5.5) .
  3. Patients with a WCC < 15.4 and Na > 135 are less likely to have necrotising fasciitis (LR - 0.13) .
  4. Patients with no history of iv drug misuse (LR - 0.41) or illicit drug injection (LR - 0.45) are less likely to have necrotising fasciitis.
Wall et al: Journal of the American College of Surgeons 2000; 191 : 227-231
Expires October 2004

The study

Setting: university hospital, USA

359 patients (aged mean 44, 64% male) admitted to hospital with a soft-tissue infection
All patients with necrotising fasciitis received iv fluid resuscitation, broad-spectrum antibiotics and surgical debridement.
Independent unblinded reference standard, applied in ?all patients from a ?consecutive inappropriate spectrum.
Reference standard:
  • necrotic fascia or muscle at operation; or follow-up
Diagnostic test: Validation of a clinical prediction guide: necrotising fascitis diagnosed if any of
  • admission white cell count > 15.4 x 10 9
  • admission serum Na < 135 mmol/l

  • 'Hard' clinical signs for necrotising fasciitis were systolic blood pressure < 90 mmHg, bullae, necrotic skin, gas on X-ray

The evidence

pre-test probability of necrotising fasciitis: 8.6%, (95% CI: 5.7% to 11.5%)

diagnostic test necrotising fasciitis other soft tissue infection LR+
(95% CI)		 post-test probability LR-
(95% CI)		 post-test probability
WCC > 15.4 or Na < 135 or both 28 80 3.7
(3.0 to 4.6) 		26% 0.13
(0.044 to 0.38) 		1.2%
1 'hard' sign for necrotising fasciitis 12 23 5.5
(3.1 to 10) 		34% 0.66
(0.50 to 0.87) 		6%
iv drug misuser 22 98 2.4
(1.8 to 3.1) 		18% 0.41
(0.24 to 0.72) 		4%
history of hepatitis 6 23 2.8
(1.2 to 6.3) 		21% 0.87
(0.73 to 1.03) 		8%
upper extremity affected 15 56 2.8
(1.8 to 4.4) 		21% 0.62
(0.44 to 0.88) 		6%
illicit drug injection 21 92 2.4
(1.8 to 3.3) 		91% 0.45
(0.27 to 0.75) 		4%
total 31 328

Comments

  1. The study spectrum reflects a population with more severe infections - 46% of patients without necrotising fasciitis underwent at least one operative debridement.
  2. Retrospective chart review
  3. By only comparing patients with confirmed diagnoses, the test characteristics appear better than in reality.
  4. 13% of patients with necrotising fasciitis died before discharge (95% CI: 1% to 25%).
  5. Diabetes, cancer or HIV did not help predict necrotising fasciitis.

Citation

  1. Wall DB, Klein SR, Black S, et al: a simple model to help distinguish necrotizing fasciitis from non-necrotizing soft tissue infections. Journal of the American College of Surgeons 2000; 191 : 227-231
Search Terms: from ACP Journal Club other articles noted
Contributor: Chris Ball, October 2001
Reviewer: Clare Wotton

Clinical Question.
Patient
Intervention or Exposure
Outcome