Performance and Clinical Utility of Follow-Up Blood Cultures in the NICU: A 10-Year Retrospective Study

Background Persistent bacteraemia is rare in adults with gram-negative rod (GNR) infections when appropriate antimicrobial therapy is administered, and routine follow-up blood cultures (FUBCs) are not generally recommended. However, neonates in the neonatal intensive care unit (NICU) have unique immunological vulnerabilities and device-related risks that may predispose them to persistent bacteraemia. Nonetheless, evidence regarding the use of FUBCs in this population remains limited. In this study, we aimed to evaluate the performance and clinical value of FUBCs in neonates with positive blood culture results. Methods A retrospective observational study of neonates admitted to the NICU of Japanese Red Cross Kyoto Daiichi Hospital between January 2015 and March 2024 was conducted. Patients with contaminated cultures were excluded from the study. Demographic variables, causative organisms, intravascular device use, meningitis, mortality within 30 days, and steroid exposure were also obtained. FUBC was defined as a repeat culture obtained ≥ 24 h after the initial positive culture. The clinical characteristics of the FUBC-positive and FUBC-negative groups were compared. FUBC performance, positivity rates by organism, and time to culture clearance were analysed. Results Among 2,569 blood culture samples, 103 were positive, and 68 cultures from 51 patients were included after excluding contaminants. FUBCs were conducted in 61 cases (89.7%), of which 18 (29.5%) were positive for the same organism. The presence of intravascular indwelling devices was significantly associated with FUBC positivity. Among gram-positive cocci, methicillin-resistant Staphylococcus aureus showed a 100% positivity rate, while Group B Streptococcus (GBS) and early onset bacteraemia showed 0% positivity. Among the GNR, Escherichia coli showed persistent bacteraemia in all FUBC-positive cases. The median time to blood culture clearance was 5.5 days. Conclusions The FUBC positivity rate of patients in NICU was higher than that reported in adult populations. FUBCs may be valuable for infants with intravascular devices, while routine FUBCs may not be necessary for early onset or GBS bacteraemia. Further multicentre studies are required to define evidence-based NICU-specific FUBC strategies.