118 Association Between Time to Gram Stain Positivity and True Bacteremia in Pediatric Emergency Department Patients: A Retrospective Cohort Study

Abstract Background Febrile children with positive blood cultures require prompt intervention due to the risk of true bacteremia. However, approximately half of the pediatric positive blood cultures are contaminants. Objectives We investigated the relationship between the time to Gram stain positivity and the likelihood of true bacteremia among children with positive blood culture drawn in the emergency department (ED). Design/Methods This was a secondary analysis of a retrospective cohort study using data from 2018 to 2024. Participants were all children with positive blood cultures in a tertiary pediatric ED. True bacteremia was defined using a standardized two-step approach, which involved identifying the bacteria responsible and assessing the clinical outcome as evaluated by two independent examiners. We investigated the correlation between the time to Gram stain positivity and the likelihood of true bacteremia by comparing the median time for positivity for the two groups, then we reported probability of bacteremia according to the timing of positivity. Results Of the 487,222 children presenting to the ED, 746 had positive blood cultures, with 368 (49.3%; 95% CI 45.8% to 52.9%) classified as true bacteremia. The median time to Gram stain positivity was significantly shorter for true bacteremia (14 hours) compared to contaminants (19 hours) (difference: 5 hours; 95%CI: 4-6 hours). The probability of bacteremia varied from 94% for cultures positive in less than 10 hours to 19 % for cultures positive after 48 hours of incubation. Nearly 90% of true bacteremia tested positive within 24 hours. Seven cases (2%) of bacteremia were identified with a time to positivity exceeding 48 hours and none of these patients were immunocompromised. The three longest delays were 72, 88 and 120 hours respectively. Conclusion There is a strong association between time to Gram stain positivity and the probability of true bacteremia in children with positive blood cultures, providing a useful indicator for distinguishing true bacteremia from contaminants. Given that most true bacteremia is detected within 24 hours, adopting a time-based approach could streamline hospital decisions and improve management. Although rare cases with extended positivity exist, the median time to positivity remains a practical marker for guiding clinical decisions.