Elsevier

Journal of Surgical Research

Volume 243, November 2019, Pages 108-113
Journal of Surgical Research

Emergency surgery
NSTI Organisms and Regions: A Multicenter Study From the American Association for the Surgery of Trauma

https://doi.org/10.1016/j.jss.2019.05.006Get rights and content

Abstract

Background

Conflicting data on the microbiology and epidemiology of necrotizing soft tissue infections (NSTIs) appear to stem from the heterogeneity in microbiology observed in regions across the United States. Our goal was to determine current differences in organism prevalence and outcomes for NSTI and non-necrotizing severe soft tissue infections across the United States. We hypothesized that there were geographical differences in organism prevalence that would lead to differences in outcomes.

Materials and Methods

This study was a retrospective multi-institutional trial from centers across the United States and Canada. Demographic, clinical, and outcomes data were collected. Bivariate and multivariable analyses were performed to determine the effects of region and microbiology on outcomes.

Results

A total of 622 patients were included in this study. Polymicrobial infections (45%) were the most prevalent infections in all regions. On bivariate analysis, Clostridium and polymicrobial infections had higher mean Laboratory Risk Indicator for Necrotizing Fasciitis scores and American Association for the Surgery of Trauma grades (P < 0.001 for both) than other organisms. Patients in the South were more likely to be uninsured and had worse unadjusted outcomes. In a risk-adjusted model, increasing American Association for the Surgery of Trauma grade was predictive of mortality (OR, 2.3; 95% CI, 1.6–3.1; P < 0.001), as was age ≥ 55 y (OR 2.7, 95% CI 1.3–5.3, P = 0.006), but region and organism type were not associated with mortality.

Conclusions

We found important regional differences with respect to organism type and demographics. However, on risk-adjusted models, neither region nor organism type predicted mortality.

Introduction

Necrotizing soft tissue infections (NSTIs) are rare but rapidly progressing and often life-threatening infections characterized by fulminant tissue destruction, signs of toxicity, and high mortality, ranging anywhere from 16 to 34%.1, 2 The Centers for Disease Control and Prevention reports that there are 500 to 1000 new cases of NSTIs yearly in the United States, with an incidence of 0.4 per 1000 persons per year.2, 3 The actual incidence of NSTI is difficult to determine, given the multiple terms used to describe this clinical entity, which is classified by anatomical region, depth of invasion, or the microbial source of infection.4

NSTIs traditionally have been classified into three types. Type I infections, the most common (≥80%), are polymicrobial and usually involve a mix of aerobic (commonly Streptococci) and anaerobic (commonly Bacteroides) bacteria. The presence of multiple pathogenic organisms at the nidus of infection may represent an underlying failure of host immunity, as most patients with type I infections are diabetic or have peripheral vascular disease.3, 5, 6 Type II (10-15% of infections) is a monomicrobial infection caused by group A Streptococcus alone or in association with Staphylococcus aureus. Frequently, there is a history of recent trauma or intravenous drug abuse in type II infections, which affect otherwise healthy, young, immunocompetent hosts.3, 5 Type III infections (<5% of cases) are caused by Clostridia species (resulting from deep penetrating wound or crush injuries) or associated with exposure to water-borne agents (Vibrio vulnificus or Aeromonas hydrophila) and are seen in patients with underlying liver disease. Rarely, NSTI can be due to fungi (Rhizopus, Mucor, and Rhizomucor), resulting in rhino-orbital-cerebral infections.

Conflicting data on the microbiology and epidemiology of NSTI appear to stem from the heterogeneity in microbiology observed in regions across the United States, even with substantial variation observed in institutions in the same metropolitan area.7 For example, in King County (Northwest), a majority of NSTIs were caused by clostridia infections, some of which was related to injection of black tar heroin.8 However, more than half of the remaining infections were caused by at least four different organisms. In a multicenter retrospective review of patients presenting with NSTI in Texas, methicillin-resistant Staphylococcus aureus was the most common pathogen among monomicrobial infections, but nearly two-thirds of monomicrobial infections involved a wide spectrum of other pathogens.7 It is posited that the variation in microbial pathogens is secondary to a combination of local environmental factors, local and regional referral patterns, and population characteristics; however, there are a paucity of national data.4 Our goal was to determine current differences in organism prevalence and outcomes for NSTI and non-necrotizing severe soft tissue infections (STIs) across the United States. We hypothesized that there were geographical differences in organism prevalence that would lead to differences in outcomes.

Section snippets

Methods

We conducted a multicenter retrospective cohort study as a project under the auspices of the American Association for the Surgery of Trauma (AAST) Patient Assessment Committee. We previously reported the primary findings of this study, an assessment of the validity of the AAST grades of STI9; as such, the patient cohort included a spectrum of disease severity, from severe cellulitis through deep tissue space infections. In this secondary analysis, we report the microbiologic findings from this

Results

Twelve centers contributed data for this study. 75% of centers were considered academic teaching hospitals. 75% were located in urban centers, 8% were suburban, 8% were considered rural, and 9% were other. Academic centers had a mean of 13 surgeons (±5.6) and 878 beds (±570). Nonteaching hospitals had a mean of nine surgeons (±2) on staff and 372 beds (±218). There were no statistical difference between academic and nonacademic centers with respect to number of surgeons and beds at

Conclusion

This observational study looking at twelve different centers from various regions (two from the South, four from the West, three from the central states and providences, and three from the Northeast) demonstrated a wide variation of microbial organisms, with as many as twenty-eight identified species. The twelve centers included in this study were volunteering centers associated with the AAST. Polymicrobial infections (type 1) were the most prevalent appreciated in all regions (Figure). Type 1

Acknowledgment

Authors' contributions: A.L., S.S., and M.C. conceived of the study; A.L., S.S., G.H.U., and M.C. entered data; S.S., G.H.U., S-W.L., and M.C. analyzed data; A.L. and M.C. authored the manuscript; S.S., G.H.U., and M.C. edited the manuscript.

References (11)

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