Differential effect of prior β-lactams and fluoroquinolones on risk of bloodstream infections secondary to Pseudomonas aeruginosa

Abstract Objective This retrospective case–control study examines risk factors for bloodstream infections (BSI) due to Pseudomonas aeruginosa (PSA). Methods Hospitalized adults with Gram-negative BSI at Palmetto Health from 2010 to 2015 were identified. Multivariate logistic regression was used to examine PSA BSI risk factors. Results Seventy and 910 patients with PSA and Enterobacteriaceae BSI, respectively, were included. Prior use of β-lactams (adjusted odds ratio [aOR] 3.9, 95% confidence intervals [CI]: 2.3–6.9), but not fluoroquinolones (aOR 1.0, 95% CI: 0.4–2.2), was a risk factor for PSA BSI. Immune compromised status (aOR 3.7, 95% CI: 2.0–6.7), respiratory source (aOR 4.4, 95% CI: 2.1–8.9), and prolonged hospitalization (aOR 1.9, 95% CI: 1.1–3.5), were predictors of PSA BSI. Conclusions Determination of class of previously used antibiotics among other clinical variables helps identify patients at risk of PSA BSI and offers opportunities to optimize empirical antimicrobial therapy.