Determinants of time to positivity in bloodstream infections: an analysis of a population-based cohort in Queensland, Australia

TL;DR

This study examines factors influencing the time it takes for bacteria to grow in blood cultures, finding that age, sex, and health conditions like liver disease and cancer affect this time.

Contribution

The study identifies host characteristics influencing time to positivity in bloodstream infections, offering insights into its potential as a prognostic marker.

Findings

Male sex is associated with slightly higher time to positivity in blood cultures.

Liver disease and malignancy are linked to shorter time to positivity.

Hospital-acquired infections show longer time to positivity compared to community-acquired ones.

Abstract

Time to Positivity (TTP) measures the interval from incubation to bacterial growth detection in blood cultures. Although shorter TTP is associated with higher mortality, factors associated with TTP remain uncertain.

A retrospective cohort study was conducted among Queensland residents with positive blood cultures between 2000–2019. Incident bloodstream infections (BSIs) were identified using Pathology Queensland data, with demographic, clinical, and outcome data linked to state-wide databases.

The study analysed 84,341 patients with monomicrobial BSI with a median patient age of 65.6 years (IQR 45.4–78.1), and most infections being community-associated (77.0%). Age showed a non-linear relationship with TTP, and male sex was linked with slightly higher TTP (Incidence Rate Ratio (IRR) 1.01; 95% Confidence Intervals (CI) 1.00–1.02; p = 0.011), reflecting a small but measurable association. Liver disease and malignancy were associated with lower TTP (IRR 0.93; 95% CI 0.91–0.95; p < 0.0001 and IRR 0.95; 95% CI 0.94–0.97; p < 0.0001 respectively), whilst diabetes showed no significant difference (IRR 1.01; 95% CI 1.00–1.02; p = 0.0840). Hospital onset infections exhibited longer TTPs (IRR 1.09; 95% CI 1.08–1.10; p < 0.0001).

There are several host characteristics associated with TTP that may in part explain the complex relationship between this variable and mortality. Beyond microbiological factors such as isolate type, TTP is also influenced by clinical variables including patient demographics and infection characteristics highlighting its potential as a prognostic marker. Further evaluation is needed to clarify its role in predicting patient outcomes and guiding tailored treatment strategies.

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