Blood culture time-to-positivity can identify S aureus, but not Enterococcal or Streptococcal endocarditis.

<ns3:p>Background International guidelines for <ns3:italic>S aureus</ns3:italic> bacteraemia often recommend screening echocardiography irrespective clinical factors that influence the likelihood of endocarditis, but this is not the case for enterococci or streptoccoci that are also high risk organism. Time to blood culture positivity (TTP) reflects bacterial load and has the potential to identify patients at higher risk of endocarditis. Methods We performed a retrospective analysis of clinical data that have been performed in a tertiary hospital in England. We investigate time to positivity (TTP) as a predictor variable in our <ns3:italic>S. aureus</ns3:italic>, enterococci and streptococci in logistic regression models and assess non-linearity of this affect using generalised additive models. We calculate NPV for TTP beyond the median value. Results The odds ratio for endocarditis from <ns3:italic>S. aureus</ns3:italic> bacteria was 0.92 (95%CI 0.85-0.99, p = 0.02) for each hour increase in TTP, with a negative predictive value of TTP greater than the median being 90% (95% CI 85-95%). For streptococci the OR was 1.02 (95%CI 0.98-1.06, p:0.31) and enterococci 1.08 (95% CI 0.99-1.18, p = 0.1) for every increase in hour of TTP. Conclusion Longer TTP is associated with lower risk of endocarditis in <ns3:italic>S. aureus</ns3:italic> bacteraemia, at 8% reduction per hour, giving an NPV of 90% beyond 13 hours. There was no evidence of association with enterococci or streptococci.</ns3:p>