Importance: Treatment of patients with infections due to Pseudomonas aeruginosa has been complicated by increased antibiotic resistance rates, which contribute to delayed appropriate treatment and deleterious outcomes.
Objective: To develop 2 clinical risk scores based on variables available at clinical presentation to estimate the risk of carbapenem resistance (CR) or extensive β-lactam resistance (EBR) among hospitalized, adult patients with P aeruginosa infections.
Design, setting, and participants: This retrospective cohort study included adult (age, ≥18 years) members of Kaiser Permanente Southern California (KPSC) with a P aeruginosa infection during hospitalization from September 1, 2011, through August 31, 2016, who received antibiotic therapy within 2 days of the culture date. Data were analyzed from July 2, 2017, through August 15, 2018.
Exposures: Demographic, clinical, and laboratory covariates 1 year before the index culture date were evaluated.
Main outcomes and measures: Pseudomonas aeruginosa was categorized as antibiotic susceptible, CR, or EBR (nonsusceptibility to carbapenems, ceftazidime, and combined piperacillin sodium and tazobactam sodium). Patients were randomly split (1:1) into training and validation data sets. The training data set was used to develop 2 prediction models using high-performance logistic regression with variable selection by Schwarz-Bayesian criterion. The models were translated into risk scores, with risk score points equaling the weighted sums of regression coefficients from the prediction model. The patient's risk was estimated as the inverse logit of the risk score.
Results: Of the 7775 patients with 11 502 P aeruginosa infections included in the analysis, most were male (4308 [55.4%]) and non-Hispanic white (3927 [50.5%]). The mean (SD) age was 70.3 (15.5) years. Among 11 502 P aeruginosa infections, 2324 (20.2%) were CR, 9178 (79.8%) were non-CR, 1033 (9.0%) were EBR, and 10 469 were non-EBR (91.0%). The strongest predictors of resistance in the CR and EBR models were history of CR P aeruginosa infection (odds ratios [ORs], 8.80 [95% CI, 6.74-11.49] and 5.04 [95% CI, 3.88-6.54], respectively), tracheostomy (ORs, 3.49 [95% CI, 2.92-4.16] and 3.13 [95% CI, 2.50-3.91], respectively), and carbapenem use in the prior 30 days (ORs, 4.18 [95% CI, 3.29-5.31] and 2.26 [95% CI, 1.74-2.93], respectively). The models for CR and EBR performed well, with areas under the receiver operating characteristics curve of 0.81 or greater for the training and validation data sets.
Conclusions and relevance: The findings of this study suggest that parsimonious risk scores can aid physicians in appropriate treatment selection during the critical period when P aeruginosa infection is suspected but antibiotic susceptibility results are not yet available.