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Updated: Jun 9, 2025
Preparation of a Blood Culture Pellet for Rapid Bacterial Identification and Antibiotic Susceptibility Testing
Published on: October 15, 2014
Time to positivity of blood cultures in paediatric patients
Catrin Kar Yee Kong1, Natalie Woon Hui Tan2, Karen Donceras Nadua2
1Department of Paediatric Medicine, KK Women's and Children's Hospital, Singapore.
Insights
A 36-hour monitoring period for blood cultures (BC) in children is sufficient to detect over 97% of pathogenic bacteria. Aerobic cultures showed faster detection times than anaerobic cultures for common pediatric pathogens.
Area of Science:
- Clinical Microbiology
- Pediatric Infectious Diseases
- Diagnostic Bacteriology
Background:
- Continuous monitoring of blood culture (BC) systems aids rapid microbial detection.
- Understanding time to positivity (TTP) variations is crucial for optimizing diagnostic protocols in pediatric care.
Purpose of the Study:
- To analyze differences in TTP for various organisms in BACTEC blood cultures.
- To evaluate if a 36-hour incubation period is adequate for detecting relevant pathogenic bacteria in pediatric patients.
Main Methods:
- Retrospective audit of positive aerobic (AE) and anaerobic (AN) BC from pediatric inpatients (August 2016 - January 2019).
- Analysis of the first positive BC per bacteraemia episode, focusing on TTP.
- Categorization of detected organisms including Gram-negative rods (GNR), Gram-positive cocci (GPC), and contaminants.
Main Results:
- A total of 480 first positive BC were analyzed from 372 bacteraemia episodes.
- Median TTP was 13.20 hours for AE and 13.92 hours for AN cultures.
- Gram-negative rods (GNR) were the most common pathogens (49.7%). Streptococcus agalactiae and Escherichia coli exhibited the fastest TTP.
- A 36-hour cutoff detected >97.7% of pathogens in AE BC and >99.1% in AN BC, compared to 86.5% of contaminants in AE BC.
Conclusions:
- Gram-negative rods (GNR) are the predominant pathogens in pediatric blood cultures.
- Aerobic (AE) blood cultures demonstrate faster pathogen detection compared to anaerobic (AN) cultures.
- A 36-hour incubation period is effective for capturing the vast majority of clinically significant bacterial pathogens in pediatric blood cultures.
Aim:
Continuous monitoring of blood culture (BC) systems allows rapid detection of microbial growth. We aimed to determine differences in time to positivity (TTP) in BACTEC BC between organisms and whether a 36-h period was sufficient to detect all relevant pathogenic bacteria for children admitted to a tertiary care paediatric hospital.
Methods:
This was a retrospective audit of positive aerobic (AE) and anaerobic (AN) BC from paediatric inpatients with available TTP from 1 August 2016 to 2 January 2019. First positive BC per bacteraemia episode was analysed.
Results:
Overall, 649 BC were positive, of which 480 first positive BC were analysed: 246 AE (51.3%) only, 216 paired (45%) (108 AE and 108 AN) and 18 AN (3.8%) only. There were 372 episodes of bacteraemia in 340 patients. Median age was 19 months (interquartile range (IQR): 1.25-60). Median TTP for AE and AN cultures was 13.20 (IQR: 9.84-18.48) and 13.92 h (IQR: 10.32-17.04), respectively. Organisms were GNR 49.7%, GPC 29.6%, contaminants 14.5%, mixed 3.0%, other 2.4% and yeast 0.8%. Streptococcus agalactiae had the fastest median TTP in AE and AN cultures, followed by Escherichia coli (AE 8.88 vs. 10.20 h). For paired AE and AN cultures, TTP was faster for AE versus AN cultures (13.36 vs. 14.52 h, P = 0.001). A 36-h cut-off time captured 97.7% AE BC and 99.1% AN BC with pathogens, and 86.5% AE BC and 91.7% AN BC with contaminants, respectively.
Conclusions:
GNR were the commonest pathogens in paediatric BC and faster growth was detected in AE versus AN cultures. By 36 h, >97.7% of BC were positive for pathogens versus 86.5% for contaminants.
