Predictors of Blood Culture Ordering and Results for Febrile Infants Aged 91 to 365 Days in the Emergency Department

Introduction The risk of invasive bacterial infections has dropped significantly among febrile infants due to widespread vaccination efforts. In older infants (age 91 days and older), diagnostic guidance is limited, and blood culture ordering is based on clinical judgment. We sought to evaluate blood culture ordering practice, bacteremia incidence, and the patient characteristics of true positive blood culture results. Methods We conducted a retrospective cohort study of febrile pediatric patients aged 91 to 365 days who presented to Kaiser Permanente Northern California emergency departments (EDs) between January 1, 2018, and December 31, 2019, who had blood cultures drawn. We identified variables related to blood culture ordering using a generalized linear mixed model and adjudicated all positive results to determine rates of true bacteremia or contamination, as well as clinical characteristics of children with true positive bacteremia. Results Among 5543 febrile infants, 611 (11.0%) underwent blood culture testing. After adjustment for covariates, higher ED temperature (adjusted odds ratio [aOR] 1.40, 95% CI, 1.30 to 1.50), presence of comorbidities (aOR 2.55, 95% CI, 2.00 to 3.25), and younger age (aOR 0.996, 95% CI, 0.995 to 0.998, P < .001) were associated with blood culture ordering. Of the 37 (6.1%) positive blood cultures, only 16 (2.6%) were true positives. All true positives occurred in infants with either an identifiable risk factor or a clinically evident source of infection. There were no cases of occult bacteremia identified. Conclusion In febrile infants aged 91 to 365 days, true bacteremia was rare and associated with significant comorbidities or an obvious infectious source. Our findings suggest a more directed approach to ED blood culture ordering.