We examined factors associated with follow-up blood cultures (FU-BCs) in patients with monomicrobial gram-negative bloodstream infection (GN-BSI), and investigated impact of FU-BCs on therapeutic management and patient outcome.
Retrospective cohort analysis of adult patients diagnosed with GN-BSI at tertiary-care university hospital, during 2013-2016. FU-BCs performed between 24 hours and 7 days after index-BCs was the exposure variable. Risk factors for 30-day mortality were analysed using multivariate Cox analysis on overall cohort, including FU-BCs as time-varying covariate, and on 1:1 matched patients according to SOFA score and time to FU-BCs.
In 278 out of 1,576 (17.6%) patients, FU-BCs were performed within a median of 3 and 2 days after index-BCs and active antibiotic therapy initiation. Persistent BSI was found in 107/278 (38.5%) patients. FU-BCs were performed in more severely-ill patients, with non-urinary sources, difficult-to-treat pathogens, and receiving initial inappropriate therapy. Source control and infectious disease consultation rates were higher among patients with preceding FU-BCs, and was associated with longer treatment duration. Thirty-day mortality was 10.4%. Independent risk factors for mortality were Charlson [hazard ratio (HR) 1.12], SOFA (HR 1.11), septic shock (HR 2.64), urinary source (HR 0.60), central-venous-catheter source (HR 2.30), complicated BSI (HR 2.10), carbapenem resistance (HR 2.34), active empiric therapy (HR 0.68), source control (HR 0.34), and FU-BCs (HR 0.48). Association between FU-BCs and lower mortality was confirmed in the 274 matched pairs.
FU-BCs were performed in more severe GN-BSIs yielding high rate of persistent BSI. In this context, FU-BCs were associated with lower mortality.

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