A Clinical Decision Tree to Predict Whether a Bacteremic Patient Is Infected With an Extended-Spectrum β-Lactamase-Producing Organism

Abstract

Background: Timely identification of extended-spectrum β-lactamase (ESBL) bacteremia can improve clinical outcomes while minimizing unnecessary use of broad-spectrum antibiotics, including carbapenems. However, most clinical microbiology laboratories currently require at least 24 additional hours from the time of microbial genus and species identification to confirm ESBL production. Our objective was to develop a user-friendly decision tree to predict which organisms are ESBL producing, to guide appropriate antibiotic therapy.

Methods: We included patients ≥18 years of age with bacteremia due to Escherichia coli or Klebsiella species from October 2008 to March 2015 at Johns Hopkins Hospital. Isolates with ceftriaxone minimum inhibitory concentrations ≥2 µg/mL underwent ESBL confirmatory testing. Recursive partitioning was used to generate a decision tree to determine the likelihood that a bacteremic patient was infected with an ESBL producer. Discrimination of the original and cross-validated models was evaluated using receiver operating characteristic curves and by calculation of C-statistics.

Results: A total of 1288 patients with bacteremia met eligibility criteria. For 194 patients (15%), bacteremia was due to a confirmed ESBL producer. The final classification tree for predicting ESBL-positive bacteremia included 5 predictors: history of ESBL colonization/infection, chronic indwelling vascular hardware, age ≥43 years, recent hospitalization in an ESBL high-burden region, and ≥6 days of antibiotic exposure in the prior 6 months. The decision tree's positive and negative predictive values were 90.8% and 91.9%, respectively.

Conclusions: Our findings suggest that a clinical decision tree can be used to estimate a bacteremic patient's likelihood of infection with ESBL-producing bacteria. Recursive partitioning offers a practical, user-friendly approach for addressing important diagnostic questions.

Keywords: ESBL; bacteremia; carbapenem; machine learning; prediction.

© The Author 2016. Published by Oxford University Press for the Infectious Diseases Society of America. All rights reserved. For permissions, e-mail journals.permissions@oup.com.

Figures

Figure 1.

Distribution of recent international healthcare exposure among extended-spectrum β-lactamase (ESBL)–positive cases: 57 of 194 ESBL-positive patients had a recent international healthcare exposure, defined as hospitalization for 1 or more nights outside the United States in the 6 months preceding ESBL bacteremia. Abbreviation: UAE, United Arab Emirates.

Figure 2.

Clinical decision tree to predict a bacteremic patient's likelihood of infection with an extended-spectrum β-lactamase (ESBL)–producing organism at the time of organism genus and species identification. Gray-shaded terminal nodes indicate that the tree would classify patients as ESBL positive, and accompanying percentages (derived from terminal node impurities) reflect the probability that patients assigned to a given terminal node are ESBL positive. Terminal node numbering (1–6) is included in parentheses. *Latin America (excluding the Caribbean), the Middle East (including Egypt), South Asia, China, and the Mediterranean.