Impact of 24/7 blood culture processing on diagnostic turnaround times and delays in effective and optimal antimicrobial therapy in bloodstream infections: a retrospective cohort study

Abstract

Background: Rapid blood culture diagnostics enable early targeted antimicrobial therapy, but microbiology laboratories rarely process signal-positive blood cultures 24/7. Our HUS Diagnostic Center Bacteriology laboratory started processing signal-positive blood cultures 24/7 in February 2021 and in February 2022 we implemented a molecular rapid diagnostic test (mRDT) into our workflow.

Objectives: We aim to show how these changes impacted blood culture turn-around-times (TAT) and patient care in the capital region of Finland.

Methods: We performed a retrospective cohort study of adult patients with positive blood cultures treated in HUS healthcare units from January 2019 to December 2023. We identified eligible patients from our laboratory information systems, and our final cohort included 15311 patients divided into three groups: pre-intervention group (January 2019-January 2021), 24/7 group (February 2021-January 2022), mRDT group (February 2022-December 2023). We compared the groups in terms of diagnostic TATs, and treatment outcomes.

Results: The median TAT for microbial identification decreased from initial 39h to 19h (p < 0.001), and for antimicrobial susceptibility testing result from 45h to 36h (p < 0.001). For resistant phenotype isolates the median time to effective antimicrobial therapy decreased from 34h to 21h (p < 0.001). Median time to optimal antimicrobial therapy for Staphylococcus aureus decreased from 45h to 28h (p < 0.001).

Conclusion: Combining 24/7 workflow with a mRDT provides substantial reductions in blood culture TATs. However, a minority of patients benefited from the rapid diagnostics in terms of effective therapy initiation, and early antimicrobial therapy optimization requires active antimicrobial stewardship.

Keywords: 24/7; antimicrobial stewardship; blood culture; bloodstream infection; rapid diagnostic test.