To determine the association between bacteremia and vaccination status in children aged 2-36 months presenting to a pediatric emergency department.
Retrospective cohort study of children aged 2-36 months with blood cultures obtained in the pediatric emergency department between January 2013 and December 2017. The exposure of interest was immunization status, defined as number of H. influenzae type B (Hib) and S. pneumoniae vaccinations, and the main outcome positive blood culture. Subjects with high-risk medical conditions were excluded.
Of 5534 encounters, 4742 met inclusion criteria. The incidence of bacteremia was 1.5%. The incidence of contaminated blood culture was 5.0%. The RR of bacteremia was 0.79 (95% CI 0.39-1.59) for unvaccinated and 1.20 (95% CI 0.52-2.75) for undervaccinated children relative to those who had received age-appropriate vaccines. Five children were found to have S. pneumoniae bacteremia and one child had Hib bacteremia; all of these subjects had at least three sets of vaccinations. No vaccine preventable pathogens were isolated from blood cultures of unvaccinated children. We found no S. pneumoniae or Hib in children 2-6 months of age who were not fully vaccinated due to age (95% CI 0-0.13%) and the contamination rate in this group was high compared with children 7-36 months (6.6% vs 3.7%).
Bacteremia in young children is an uncommon event. Contaminated blood cultures were more common than pathogens. Bacteremia from S. pneumoniae or Hib is uncommon and, in this cohort, was independent of vaccine status.

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