Risk factors for pneumonia due to beta-lactam-susceptible and beta-lactam-resistant Pseudomonas aeruginosa: a case-case-control study.

Purpose: This case-case-control study aims to identify clinical predictors for pneumonia due to Pseudomonas aeruginosa (PA) which is (1) susceptible to all routinely tested antipseudomonal beta-lactams (APBL-S) and (2) resistant to at least one antipseudomonal beta-lactam (APBL-R).
Methods: Hospitalized adults with acute bacterial pneumonia at Palmetto Health hospitals in Columbia, SC, USA from January 1, 2012 to April 15, 2014 were identified. Multivariate logistic regression was used to determine risk factors for pneumonia due to APBL-S PA and APBL-R PA.
Results: Among 326 unique patients, 119 had pneumonia due to APBL-S PA (cases), 44 due to APBL-R PA (cases) and 163 due to ceftriaxone-susceptible bacteria (controls). Bronchiectasis [odds ratio (OR) 5.7, 95% confidence intervals (CI) 1.3-39.2], interstitial lung disease (OR 6.2, 95% CI 1.5-42.6), prior airway colonization with APBL-S PA (OR 7.2, 95% CI 1.1-139.4) and recent exposure to both antipseudomonal beta-lactam (APBL; OR 2.2, 95% CI 1.1-4.5) and nonpseudomonal beta-lactams (OR 2.6, 95% CI 1.0-6.8) were independently associated with increased risk of APBL-S PA pneumonia. Bronchiectasis (OR 8.3, 95% CI 1.7-46.6), prior airway colonization with APBL-R PA (OR 14.9, 95% CI 2.0-312.9) and recent use of only APBL (OR 7.7, 95% CI 3.4-17.9) were predictors for APBL-R PA pneumonia.
Conclusions: Stratification of hospitalized patients with pneumonia based on structural lung disease, prior airway colonization and recent antimicrobial exposure may improve empirical antimicrobial selection. Expansion of antimicrobial regimen from ceftriaxone to APBL or combination therapy is suggested in patients with risk factors for APBL-S or APBL-R PA, respectively.