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. 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 S. aureus bacteremia 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 S. aureus bacteremia (23/1703 MRSA) in 1610 patients were included. Median age was 75 years (interquartile range [IQR] 63-84) and median Charlson comorbidity index 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 [IQR 10-18] hours, p<0.001). The risk of endocarditis decreased with 11% per hour (OR 0.89 [95% CI 0.54-0.92] p<0.001) 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<0.001). 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 S. aureus bacteremia.