Time to Staphylococcus aureus Blood Culture Positivity as a Risk Marker of Infective Endocarditis: A Retrospective Cohort Study.

BACKGROUND

Endocarditis occurs in approximately 10%-15% of patients with Staphylococcus aureus bacteremia (SAB). Short time to positivity (TTP) in blood culture flasks has been linked to endocarditis in smaller studies. This study evaluated the association between TTP and endocarditis in SAB in a large cohort.

METHODS

Adult patients with ≥1 S. aureus positive blood culture treated at a tertiary-level, 500-bed hospital in Stockholm, Sweden between 2011-2021 were retrospectively identified. The primary outcome was the presence of infective endocarditis.

RESULTS

A total of 1703 episodes of SAB (23/1703 methicillin-resistant) in 1610 patients were included. Median age was 75 (interquartile range [IQR], 63-84) years and median Charlson comorbidity index score was 2 (IQR, 1-3). Echocardiography was performed in 1102/1703 (65%). Thirty-day mortality was 406/1703 (24%) and endocarditis was found in 154/1703 (9%). Median TTP was shorter in patients with endocarditis (9 [IQR, 7-12] hours) compared to patients without endocarditis (13 [interquartile range, 10-18] hours; P < .001). The risk of endocarditis decreased with 11% per hour (odds ratio [OR], 0.89 [95% confidence interval {CI}, .54-.92]; P < .001) in a univariate analysis using TTP as a continuous variable. In multivariate analysis, TTP <13 hours (the median) was independently associated with endocarditis (OR, 3.59 [95% CI, 2.35-5.3]; P < .001). The negative predictive value of TTP >13 hours for endocarditis was 96% (95% CI, 95%-97%).

CONCLUSIONS

Short TTP was associated with endocarditis. The negative predictive value of >95% suggests that TTP >13 hours can be used to risk-stratify patients with SAB.