By Philip R. Fischer, MD, DTM&H
Synopsis: Falsely positive (contaminated) blood culture samples lead to unnecessary antimicrobial use, excessive testing, prolonged hospitalizations, and increased healthcare costs. In pediatric settings, the greatest risk of blood culture contamination is with infants younger than 1 year of age and with children in emergency department settings.
Source: Childress K, Hartmann M, Fernandes G, et al. Pediatric blood culture contamination rates and risk factors in a large integrated health system. Hosp Pediatr. 2025; Jun 13:e2024008184. doi: 10.1542/hpeds.2024-008184. [Online ahead of print].
Results of blood cultures are important to the diagnosis of bacteremia and sepsis and help guide antimicrobial therapy. However, contaminated culture samples lead to unnecessarily prolonged antibiotic use as well as to additional testing and prolonged hospitalization. In the United States, blood culture contamination is blamed for costing approximately $5 billion each year.
Most data on blood culture contamination comes from academic inpatient settings. Contamination occurs in 0.6% to 6% of samples, and 1% contamination is considered a benchmark for targeted quality improvement efforts.
To better understand blood culture contamination in pediatric patients, the authors studied contamination in a large integrated health system in northern California, the Kaiser Permanente Medical Group. Blood culture contamination was defined as the presence of one or more commensal bacterial species growing within five days of incubation of a sample taken from a patient without a condition that would predispose to significant infection by a commensal species.
The study included 89,948 samples taken from patients younger than 18 years of age from 2014 through 2022. A total of 3,039 (3.4%) samples yielded positive results, and 1,594 samples (52% of positive results, 1.8% of all blood culture samples) were deemed to be due to blood culture contamination.
Contaminated blood cultures were found in:
- 2.0% of 0- to 28-day-olds;
- 5.4% of 29- to 90-day-olds;
- 2.7% of 91- to 365-day-olds;
- 1.8% of 1- to 3-year-olds;
- 1.5% of 3- to 5-year-olds;
- 0.9% of 5- to 17-year-olds.
Contamination rates varied based on the type of staff member obtaining the blood samples:
- Nurse in emergency department 3.0%;
- Nurse not in emergency department 1.4%;
- Phlebotomist 1.1%.
A small number of “other” staff members obtaining culture samples included physicians and physician assistants. Only 0.7% of those samples were contaminated.
The setting of sampling also was related to the rate of blood culture contamination:
- Outpatient clinic 0.6%;
- Inpatient 1.3%;
- Emergency department 2.6%;
- Observation unit 2.7%.
The patient’s sex, race, and family income were not related to the rate of blood culture contamination. The presence or absence of fever also was not related to blood culture contamination.
The authors are using their findings as the basis of quality improvement projects using plan-do-study-act cycles. They are specifically looking at the effect of: prioritizing the use of phlebotomists to obtain blood culture samples; providing additional training for nurses, especially in emergency departments, about the proper techniques of blood culture sampling; and standardizing protocols for obtaining blood culture samples.
Commentary
The authors identified patient ages as well as settings and backgrounds of staff members that were related to increased rates of blood culture contamination. Improvement efforts can focus on infants, emergency department settings, and nurses.
The authors reported but did not discuss the high frequency of contaminants among positive cultures. More than half of cultures reported as positive ended up being due to contamination. This finding aligns with the clinical experience of many pediatricians and highlights the importance of improving blood culture sampling to improve antimicrobial stewardship, avoid unnecessary testing, and reduce healthcare costs.
In Canadian emergency departments, as in the California study, approximately 50% of positive blood cultures are due to contamination.1 Interestingly, physicians in the Canadian settings have divergent clinical responses to finding “positive” cultures, with 49% discharging a 9-week-old with a positive blood culture and otherwise normal blood test results and 35% keeping such a child for ongoing inpatient antimicrobial therapy.1 Clinical decision tools could help standardize care of children with positive blood cultures while awaiting microbial identification.1
In a very different setting with high-risk newborns, investigators in Izmir, Turkey, implemented a “bundle” of interventions to reduce blood culture contamination in a quaternary newborn intensive care unit.2 They were successful in reducing contamination from 12.5% to 3.8%.2 Surveys in Australia and Aotearoa (New Zealand) suggest that there is potential for helpful improvements in the quality of obtaining and processing pediatric blood culture samples in those settings as well.3
Philip R. Fischer, MD, DTM&H, is Professor of Pediatrics, Department of Pediatric and Adolescent Medicine, Mayo Clinic, Rochester, MN.
References
1. Gouin S, Carrière B, Gravel J. Management of a positive blood culture in the pediatric emergency department: A multicenter case-based survey. CJEM. 2025;27(6):470-475.
2. Çalkavur Ş, Kalkanlı OH, Ketenci T, et al. Effectiveness of a blood culture bundle in reducing contamination rates in a neonatal intensive care unit. Turk J Pediatr. 2025;67(2):135-143.
3. Duguid RC, Tanti D, Elvy JA, et al. Assessing paediatric blood culture quality: Surveys of clinician and laboratory practices in Australia and New Zealand. Pathology. 2025;57(3):361-367.
Falsely positive (contaminated) blood culture samples lead to unnecessary antimicrobial use, excessive testing, prolonged hospitalizations, and increased healthcare costs. In pediatric settings, the greatest risk of blood culture contamination is with infants younger than 1 year of age and with children in emergency department settings.
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