Correlation of antibiotic exposure with development of extreme drug resistant Acinetobacter baumannii

Introduction: Prior exposure to antibiotic therapy is a well-defined risk factor for development of multidrug resistant (MDR) and extreme drug resistant (XDR) organisms. This association is primarily due to the disruption of the normal flora by antibiotics (collateral damage). We recently developed an antibiotic exposure score, ranging from 1-5, to estimate the level of collateral damage. The objective of this study was to define if an association exists between increasing Antibiotic Exposure score and development of XDR-Acinetobacter baumannii.

Materials and Methods: We reviewed medical records of patients infected with MDR- and XDR-Acinetobacter to define antibiotics used during the prior 30 days. The population exposure (PE) score was calculated by adding all antibiotic exposure scores for all patients. Median PE scores were also calculated for MDR and XDR-Acinetobacter separately. The Mann-Whitney U test was used to compare the PE scores for MDR and XDR-Acinetobacter populations. Differences with P-values of ≤0.05 were considered statistically significant.

Results: A total of 46 patients were reviewed. The PE score for the full population was 410. The median PE score for those with MDR-Acinetobacter was 9.0 (Inter quartile Range: 6.0 to 14). The median PE score for those with XDR-Acinetobacter was 9.1 (Inter quartile Range: 4 to 13.5). There was not a significant difference between PE scores (p=0.96).

Conclusions: Antibiotic collateral damage, as measured by PE score, was not able to predict the presence of MDR/XDR-Acinetobacter. This data suggests that factors beyond antibiotic exposure are important in the evolution of Acinetobacter from MDR to XDR.