The microbiology of necrotizing soft tissue infections

Presented at the 86th Annual Meeting of the North Pacific Surgical Association, Vancouver, British Columbia, Canada, November 12–13, 1999.
https://doi.org/10.1016/S0002-9610(00)00360-3Get rights and content

Abstract

Objective: A large number of necrotizing soft tissue infections (NSTI) treated at a single institution over an 8-year period were analyzed with respect to microbial pathogens recovered, treatment administered, and outcome. Based on this analysis, optimal empiric antibiotic coverage is proposed.

Methods: A retrospective chart review of all patients with documented NSTI was conducted. Microbiologic variables were tested for impact on outcome using Fisher’s exact test and multivariate analysis by logistic regression.

Results: Review of the charts of 198 patients with documented NSTI revealed 182 patients with sufficient microbiologic information for analysis. These 182 patients grew an average of 4.4 microbes from original wound cultures, although a single pathogen was responsible in 28 patients. Eighty-five patients had combined aerobic and anaerobic growth, the most common organisms being, in order, Bacteroides species, aerobic streptococci, staphylococci, enterococci, Escherichia coli, and other gram-negative rods. Clostridial growth was common but did not affect mortality unless associated with pure clostridial myonecrosis. Mortality was affected by the presence of bacteremia, delayed or inadequate surgery, and degree of organ system dysfunction on admission.

Conclusions: NSTI are frequently polymicrobial and initial antibiotic coverage with a broad-spectrum regimen is warranted. The initial regimen should include agents effective against aerobic gram-positive cocci, gram-negative rods, and a variety of anaerobes. The most common organisms not covered by initial therapy were enterococci. All wounds should be cultured at initial debridement, as changes in antibiotic coverage are frequent once isolates are recovered.

Section snippets

Materials and methods

The data reported herein are from a single institution, a 100-bed level I trauma center serving a state and surrounding region with population exceeding 5 million people and possessing a multipatient hyperbaric chamber capable of treating 21 patients simultaneously. Between March 1985 and June 1993, 198 patients with NSTI were admitted and treated. Diagnosis was confirmed by either histologic examination or a combination of clinical, microbiologic, and gross anatomic findings. All patients had

Results

Among the 198 patients studied, mortality was 25.3%, the average age was 51.5 years, male patients accounted for 57.3% of the total, and 56.4% of patients were diabetic. The mean extent of infection was 8.4% (±0.4%) of body surface area, and the most common sites of infection were perineal sources (Fournier’s gangrene, 36% of cases), podiatric sources (15.2%), and traumatic wounds (14.7%). Table I and Table IIlist the preexisting medical conditions and sites of origins among the study patients.

Comments

This retrospective analysis of 198 cases of NSTI establishes that such infections are capable of harboring a wide variety of microbial pathogens. Most infections are polymicrobial (average 4.4 microbes per case), but single-pathogen infections are not uncommon. Beta-hemolytic streptococci are the most frequent solitary pathogens (15 of 28 cases). The most common bacterial species overall include Bacteroides/Prevotella (116 isolates), streptococci (106 isolates), and gram-negative

Conclusions

Necrotizing soft tissue infections are frequently polymicrobial and initial antibiotic coverage with a broad-spectrum regimen is warranted. The initial regimen should include agents effective against aerobic gram-positive cocci, gram-negative rods, and a variety of anaerobes. The most common organisms not covered by initial therapy were enterococci. All wounds should be cultured at initial debridement, as changes in antibiotic coverage are frequent once isolates are recovered.

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