Incubation time required for neonatal blood cultures to become positive

Authors: Jardine, Luke; Davies, Mark W; Faoagali, Joan

Source: Journal of Paediatrics and Child Health, Volume 42, Number 12, December 2006 , pp. 797-802(6)

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Abstract:

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.

Keywords: bacteriological technique; blood culture; infant; newborn; septicaemia

Document Type: Research article

DOI: http://dx.doi.org/10.1111/j.1440-1754.2006.00980.x

Affiliations: 1: Queensland Health Pathology Service, Department of Microbiology, Royal Brisbane and Women's Hospital, Brisbane, Queensland, Australia

Publication date: 2006-12-01

Incubation time required for neonatal blood cultures to become positive

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