Time to positivity of Blood Culture in Newborns Admitted to Neonatology - A Retrospective Study

Abstract

Background: Neonatal sepsis remains a significant cause of morbidity and mortality in Neonatal Intensive Care Units (NICU), requiring prompt diagnosis. Despite international recommendations advocating the discontinuation of empirical antibiotic therapy within 36-48 hours if blood cultures remain negative and the newborn is asymptomatic, the applicability of these guidelines to national clinical practice is uncertain. This study aims to analyse the time to positivity (TTP) of blood culture in newborns, to inform local antibiotic stewardship programs. Methods: This retrospective cohort study was conducted at a level III Portuguese NICU and included all neonates admitted between April 1st 2022 and December 31st 2024, with at least one positive blood culture. Results: A total of 75 eligible cultures from 67 neonates were included. The median TTP was 13.3 h (IQR 9.0-18.2) with 98.5% of positive cultures detected within 48 h. Median TTP was 10.4 h (8.2-14.8) in infants with blood cultured <72h and 14.7 h (9.6-18.7) after 72h of life. In blood cultures collected after 72h of life, median TTP was significantly shorter for confirmed sepsis than for contaminants (13.2 vs 21.6h; p<0.01). Furthermore, TTP was significantly shorter for Gram negative bacteria than for Gram positive (p<0.01) and no difference was observed in the TTP in patients with ongoing antibiotic therapy at the time of blood culture collection (p0.846). Conclusions: These findings suggest that most blood cultures in neonatal sepsis cases become positive before 48 h, supporting the early discontinuation of empirical antibiotics in asymptomatic patients.