A Pilot Analysis for a Multicentric, Retrospective Study on Biodiversity and Difficult-to-Treat Pathogens in Burn Centers across the United States (MICROBE)

Abstract

Following burn injury, patients are at increased risk of infection and are often cited as having a high incidence of difficult-to-treat pathogens (DTp). The purpose of this study is to determine the incidence of DTp after burn injury, which factors are associated with their development, and subsequent outcomes. This single-center, retrospective study assessed patients with thermal or inhalation injury who had a positive culture resulting in initiation of treatment (i.e., excision, topical, or systemic antimicrobials). Demographic data, pathogen and resistance profiles, and prior exposure to topical and systemic antimicrobials were collected. Pathogens were considered DTp if they were multi-drug-resistant (MDR), extensively drug-resistant (XDR), methicillin-resistant Staphylococcus aureus (MRSA), extended-spectrum beta-lactamase (ESBL)-producing, AmpC-producing, carbapenem-resistant, difficult-to-treat resistance (DTR) Pseudomonas sp., carbapenem-resistant Acinetobacter baumannii (CRAB), or Stenotrophomonas spp. Sixty-five patients who grew 376 pathogens were included in the final analysis. Two-hundred thirteen (56.7%) pathogens were considered DTp. Prior exposure to 7 of the 11 collected topical antimicrobials and 9 of 11 systemic antimicrobial classes were significantly associated with future development of a DTp. This remained true for six and eight, respectively, after controlling for significant covariates via logistic regression. As there were only four deaths, a Cox-proportional hazard analysis was not feasible. The Kaplan-Meier plot according to DTp revealed a clear divergence in mortality (Log rank p = 0.0583). In this analysis, exposure to topical and systemic antibiotics was associated with the development of DTp. The results from this pilot study will inform the next iteration of multicenter study.

Keywords: antimicrobial resistance; burn; difficult to treat pathogens; risk factors.

Figure 1

Flow diagram of patient screening and final cohort. N = patients screened; n = final sample of patients.

Figure 2

Antimicrobial resistance profiles for pathogens classified as DTp. DTp is a composite (show in orange) of the listed individual antimicrobial resistance profiles (shown in blue). Pathogens could meet criteria for multiple resistance categories. MDR, multi-drug resistant; XDR, extensively drug resistant; ESBL, extended-spectrum beta-lactamase; AmpC, ampicillin-resistance gene group C; CRO, carbapenem-resistant organism; DTRPse, difficult-to-treat resistance Pseudomonas spp.; CRAB, carbapenem-resistant Acinetobacter baumannii; Steno, Stenotrophomonas maltophilia; MRSA, methicillin-resistant Staphylococcus aureus.

Figure 3

Impact of exposure to topical antimicrobials prior to culture obtainment on DTp development. * denotes p < 0.05. SSD, silver sulfadiazine; CHG, chlorohexidine gluconate.

Figure 4

Impact of exposure to systemic antimicrobials prior to culture obtainment on DTp development. * Denotes p < 0.05. Non-Pse BL, non-pseudomonal beta-lactam; Anti-Pse BL, anti-pseudomonal beta-lactam; Ext Spec BLI, extended-spectrum beta-lactam beta-lactamase inhibitor; FQ, fluoroquinolone; MRSA, methicillin-resistant Staphylococcus aureus; AMG, aminoglycoside; Sulfa/Trim, sulfamethoxazole-trimethoprim; TCN, tetracycline.

Figure 5

Kaplan–Meier analysis stratified by DTp development.