December 21, 2018
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Studies inconsistently define, report contaminants in blood cultures

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Slightly more than half of studies that included blood cultures collected from children aged 0 to 36 months described the methodology used to define contaminants, according to a review published in the Journal of the Pediatric Infectious Diseases Society. Fewer than one-quarter of these studies reported the contamination rate found in samples, with rates reaching as high as nearly 23%, researchers wrote.

Contamination rates in pediatric populations have been reported to be between 1% and 11%, and higher rates are found in younger children, likely because of the technical challenges presented by their smaller veins, decreased cooperation and small sample volumes,” Laura Chappell-Campbell, MD, from the department of pediatrics at Stanford University School of Medicine, and colleagues wrote.

The researchers added that false-positives in blood cultures caused by contaminants cause a significant burden related to hospital resources, more days spent in the hospital and unneeded antibiotic use.

Of the 69 studies included in the review that were published between 1986 and 2016, contaminants were defined in 54%. Even fewer studies (23%) reported rates of contamination. According to Chappell-Campbell and colleagues, the contamination rate ranged from 0.5% to 22.8%. Most studies defined contaminants by organism species (n = 22), but 11 used multifactorial approaches and four used the patient’s clinical management.

Image of a blood culture 
Many researchers who use blood cultures in young children do not define the methodology used to define contaminants. Contamination rates can reach as high as 23% in pediatric patients, researchers wrote. 
Source: Adobe

The researchers said many common organisms — especially gram-positive cocci — were inconsistently categorized as pathogens or contaminates.

“At a minimum, our findings highlight the need for implementation of standardized publication guidelines for the consistent reporting and definitions of blood culture contaminants,” Chappell-Campbell and colleagues wrote. “Such transparency will enable better interpretation of study results and improved accuracy in comparing the prevalence and epidemiology of pediatric bacteremia across studies.” – by Katherine Bortz

Disclosures: The authors report no relevant financial disclosures.