Objective To determine the time to positivity (TTP) of blood cultures among infants with late-onset bacteraemia and predictors of TTP >36 hours.
Design Retrospective cohort study.
Setting 16 birth centres in two healthcare systems.
Patients Infants with positive blood cultures obtained >72 hours after birth.
Outcome The main outcome was TTP, defined as the time interval from specimen collection to when a neonatal provider was notified of culture growth. TTP analysis was restricted to the first positive culture per infant. Patient-specific and infection-specific factors were analysed for association with TTP >36 hours.
Results Of 10 235 blood cultures obtained from 3808 infants, 1082 (10.6%) were positive. Restricting to bacterial pathogens and the first positive culture, the median TTP (25th–75th percentile) for 428 cultures was 23.5 hours (18.4–29.9); 364 (85.0%) resulted in 36 hours. Excluding coagulase-negative staphylococci (CoNS), 275 of 294 (93.5%) cultures were flagged positive by 36 hours. In a multivariable model, CoNS isolation and antibiotic pretreatment were significantly associated with increased odds of TTP >36 hours. Projecting a 36-hour empiric duration at one site and assuming that all negative evaluations were associated with an empiric course of antibiotics, we estimated that 1164 doses of antibiotics would be avoided in 629 infants over 10 years, while delaying a subsequent antibiotic dose in 13 infants with bacteraemia.
Conclusions Empiric antibiotic administration in late-onset infection evaluations (not targeting CoNS) can be stopped at 36 hours. Longer durations (48 hours) should be considered when there is pretreatment or antibiotic therapy is directed at CoNS.
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Contributors SM and MWK conceptualised and designed the study, contributed to interpretation of results, drafted the initial manuscript, and reviewed and revised the final manuscript. DDF and SMB contributed to study design, data acquisition, interpretation of results, drafted the initial manuscript, critically reviewed the manuscript, and approved the final manuscript as submitted. MBD contributed to study design and data acquisition, performed statistical analyses, critically reviewed the manuscript, and approved the final manuscript as submitted. SAC and KMP contributed to interpretation of results, critically reviewed the manuscript and approved the final manuscript as submitted. EW, EMW and SL contributed to data collection and verification, critically reviewed the manuscript, and approved the final manuscript as submitted. SM accepts full responsibility for the work and/or the conduct of the study, had access to the data, and controlled the decision to publish.
Funding DDF receives funding from the Agency for Healthcare Research and Quality (K08HS027468). SM receives funding from the Eunice Kennedy Shriver National Institute of Child Health and Human Development from the National Institutes of Health (grant K23HD088753). SAC receives funding from the National Heart, Lung, and Blood Institute of the National Institutes of Health (T32HL007891).
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed.
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