Evaluating Blood Culture Parameters to Identify Patients at Low Risk of Infective Endocarditis Among Those With Bacteremia by Gram-positive Cocci.

Background: Identifying patients at low risk for infective endocarditis (IE) among those with bacteremia by Gram-positive cocci is critical to optimize cardiac imaging use. The aim was to assess the diagnostic performance of blood culture parameters in identifying patients at low risk for IE.

Methods: Adult patients with bacteremia due to Staphylococcus aureus, streptococci, or Enterococcus faecalis at the Lausanne University Hospital were included. Low-risk criteria were defined as: only one positive out of four initial blood culture bottles and bacteremia clearance within 48 hours. The primary outcome was the diagnosis of IE, determined by the Endocarditis Team. Negative likelihood ratios (NLRs) were calculated.

Results: Among 2165 episodes of bacteremia, 1165 (54%) were due to S. aureus, 726 (34%) to streptococci, and 326 (15%) to E. faecalis. IE was diagnosed in 561 (26%) episodes. Among all episodes, 1767 (82%) had >1 positive out of the initial 4 blood culture bottles collected, and 1783 (82%) had either >1 positive out of the initial 4 blood culture bottles or persistent bacteremia for ≥48 hours. Having only 1 positive out of 4 initial blood culture bottles was associated with a NLR of 0.10 (95% CI, .06-.18). When combining both criteria, 1 positive out of 4 blood culture bottles and bacteremia clearance before 48 hours, the NLR was 0.08 (0.05-0.15).

Conclusions: Simple blood culture parameters may help identify patients at low risk for IE. However, the approach classifies most patients as high-risk and may have limited impact on reducing echocardiography use.