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Updated: Jun 21, 2025
Preparation of a Blood Culture Pellet for Rapid Bacterial Identification and Antibiotic Susceptibility Testing
Published on: October 15, 2014
Time to Positive Blood Cultures Among Critically Ill Children Admitted to the PICU
Stephanie M Yasechko1, Margot M Hillyer2, Alison G C Smith3
1Division of Pharmacy, Cincinnati Children's Hospital Medical Center, Cincinnati, OH.
Insights
In critically ill children, 95% of significant blood cultures turned positive within 36 hours, irrespective of immune status. This suggests reassessing antimicrobial therapy and considering shorter empiric antibiotic durations for low-risk patients.
Area of Science:
- Pediatric critical care medicine
- Infectious diseases
- Clinical microbiology
Background:
- Bloodstream infections are a significant concern in critically ill children.
- Timely detection of bacteremia is crucial for effective treatment and patient outcomes.
- Understanding the time to positivity (TTP) of blood cultures can inform diagnostic and therapeutic strategies.
Purpose of the Study:
- To evaluate the time to positivity (TTP) for clinically significant blood cultures in pediatric intensive care unit (PICU) patients.
- To analyze factors influencing TTP, including pathogen type and host immune status.
Main Methods:
- A retrospective review of positive blood cultures from patients aged 0-20 years admitted to a large tertiary-care PICU.
- Analysis of TTP, defined as time from blood culture draw to initial Gram stain result.
- Stratification of TTP by host immune status (previously healthy, standard risk, immunocompromised).
Main Results:
- The median TTP for 164 episodes of bacteremia was 13.3 hours.
- By 36 hours, 95% of positive blood cultures yielded results.
- Median TTP varied by immune status (10.6 hours for immunocompromised vs. 13.2-14.0 hours for others; p=0.001), but was independent of blood volume or Gram stain type.
Conclusions:
- A high percentage (95%) of clinically significant blood cultures in critically ill children yield positive results within 36 hours.
- Findings support frequent reassessment of antimicrobial therapy needs.
- Consideration of shorter empiric antibiotic durations in low-suspicion cases is warranted.
Objectives:
Our study aimed to assess the time to positivity (TTP) of clinically significant blood cultures in critically ill children admitted to the PICU.
Design:
Retrospective review of positive blood cultures in patients admitted or transferred to the PICU.
Setting:
Large tertiary-care medical center with over 90 PICU beds.
Patients:
Patients 0-20 years old with bacteremia admitted or transferred to the PICU.
Interventions:
None.
Measurements And Main Results:
The primary endpoint was the TTP, defined as time from blood culture draw to initial Gram stain result. Secondary endpoints included percentage of cultures reported by elapsed time, as well as the impact of pathogen and host immune status on TTP. Host immune status was classified as previously healthy, standard risk, or immunocompromised. Linear regression for TTP was performed to account for age, blood volume, and Gram stain. Among 164 episodes of clinically significant bacteremia, the median TTP was 13.3 hours (interquartile range, 10.7-16.8 hr). Enterobacterales, Staphylococcus aureus, Streptococcus agalactiae, and Streptococcus pneumoniae were most commonly identified. By 12, 24, 36, and 48 hours, 37%, 89%, 95%, and 97% of positive cultures had resulted positive, respectively. Median TTP stratified by host immune status was 13.2 hours for previously healthy patients, 14.0 hours for those considered standard risk, and 10.6 hours for immunocompromised patients (p = 0.001). Median TTP was found to be independent of blood volume. No difference was seen in TTP for Gram-negative vs. Gram-positive organisms (12.2 vs. 13.9 hr; p = 0.2).
Conclusions:
Among critically ill children, 95% of clinically significant blood cultures had an initial positive result within 36 hours, regardless of host immune status. Need for antimicrobial therapy should be frequently reassessed and implementation of a shorter duration of empiric antibiotics should be considered in patients with low suspicion for infection.
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