Journal of Paediatrics and Child Health 42 (2006) 797 – 802 797 © 2006 The Authors Journal compilation © 2006 Paediatrics and Child Health Division (Royal Australasian College of Physicians) doi:10.1111/j.1440-1754.2006.00980.x Key Points 1 Incubation time for positive blood cultures significantly differs by organism type. 2 Incubation time for positive blood cultures significantly differs whether or not they are considered early or late septicaemia versus contaminants. 3 Infants who are <48 hours of age at the time of blood culture collection, who remain clinically well and have negative cultures 36 hours after the initial collection can safely have their anti- biotic treatment ceased. Correspondence: Dr Luke Jardine, Department of Neonatology, Royal Brisbane and Women’s Hospital, Butterfield Street, Herston, Brisbane, Qld 4029, Australia. Fax: +61 7 3636 5259; email: luke_jardine@health.qld. gov.au Accepted for publication 30 July 2006. ORIGINAL ARTICLE Incubation time required for neonatal blood cultures to become positive Luke Jardine, 1 Mark W Davies 1,2 and Joan Faoagali 3 1 Grantley Stable Neonatal Unit, Royal Brisbane and Women’s Hospital, 2 Department of Paediatrics and Child Health, The University of Queensland, Royal Children’s Hospital and 3 Queensland Health Pathology Service, Department of Microbiology, Royal Brisbane and Women’s Hospital, Brisbane, Queensland, Australia Aim: We aimed to determine the laboratory detection time of bacteraemia in neonatal blood cultures, and whether this differed by: organism; samples deemed to represent true bacteraemia versus contaminants; and blood cultures collected from an infant <48 h of age (early) or ≥48 h of age (late). Methods: A retrospective audit of all positive blood cultures collected from neonates in the Grantley Stable Neonatal Unit, Royal Women’s Hospital, Brisbane, between 1 January 2000 and 31 December 2004 was undertaken. The bacteraemia detection method used was the BacTAlert system with Peds bottles. Results: Two hundred and three positive blood cultures were included in the analysis. One hundred and sixteen (57%) were deemed septicaemia, 87 (43%) were deemed contaminants. The median (interquartile range) time to positivity for positive blood cultures deemed septicaemia and contaminants were 15.9 (11.6, 22.2) and 30.2 (20.4, 43.9) h, respectively. Fifty-six (28%) positive blood cultures were collected when infants were <48 h of age and 147 (72%) were collected in infants ≥48 h of age. Post hoc analysis revealed that the time to positivity for early septicaemia was 13.7 (11, 16.7) h; early contaminant was 25.2 (19.2, 33.8) h; late septicaemia was 17.2 (12.2, 23.4) h; and late contaminant was 37.9 (21.7, 51.2) h. The time to positivity for: Group B streptococcus was 9.3 (8.2, 11.0) h; Escherichia coli was 11.3 (10.0, 13.5) h; and coagulase-negative staphylococci was 28.9 (20.5, 41.2) h. Conclusion: The incubation time for positive blood cultures significantly differs by organism type and whether they are considered early or late septicaemia versus contaminants. We recommend that: infants who are <48 h of age at the time of blood culture collection, who remain clinically well and have negative cultures 36 h after the initial collection can safely have their antibiotic treatment ceased; infants who are ≥48 h of age at the time of collection should continue antibiotic treatment for at least 48 h before cessation is considered. Key words: bacteriological technique; blood culture; infant; newborn; septicaemia. neonatal septicaemia to be 38 deaths per 100 000 live births in the period 1992 through 1994. 2 Case reports of mortality rates for septic neonates range from 10% to 50%. 1,3,4 A positive blood culture is still considered the gold standard for the diagnosis of septicaemia. 5 Positive results can be influenced by a number of factors including: collection technique, volume of blood drawn, number of colony-forming units present in the blood at the time of collection and the use of intrapartum antibiotics. 5–7 Most infants who have a blood culture collected are commenced on antibiotics while results are awaited. Our current practice is to treat the infant with intravenous antibiotics for a minimum 48 h after the blood culture has been collected. The majority of babies that have blood cultures taken will not have any organisms detected and will not have septicaemia. Knowing the incubation time for the organisms that cause septicaemia will deter- mine how long it is necessary to wait for a blood culture to return a positive result (along with other information) before declaring that the baby is unlikely to have septicaemia and does not require further antibiotics. Prior to the routine use of automated blood culture incubators, Pichichero et al. reported that 96% and 98% of cultured pathogens Neonatal sepsis is a potentially life-threatening event. The incidence of early-onset neonatal sepsis has been reported as less than 1–8.1 cases per 1000 live births. 1 Stoll et al. found the mortality rate of