Occult bacteremia from a pediatric emergency department: current prevalence, time to detection, and outcome.

OBJECTIVE: To evaluate selected characteristics of occult bacteremia in the post-Haemophilus influenzae type b (HIB) vaccine era.
METHODS: A retrospective cohort study was performed involving 5901 children 2 to 24 months old with fever >/=39.0 degrees C evaluated with a blood culture at an urban tertiary care children's hospital emergency department (ED) between February 1993 and June 1996. Patients were excluded if immune-suppressed, diagnosed with a focal infection, evaluated by lumbar puncture, or admitted to the hospital during initial evaluation. Prevalence of occult bacteremia, distribution of current pathogenic organisms, and time to positive culture in a continuously monitored system were determined. All patients with cultures positive for pathogenic bacteria were reevaluated and serious adverse outcomes were documented.
RESULTS: The prevalence of occult bacteremia was 1.9% (95% confidence interval: 1.5%-2.3%). Streptococcus pneumoniae accounted for 82.9% of all pathogens and H influenzae was not a causative organism in this cohort. The mean time to positive culture was significantly shorter for pathogens compared with contaminants (14.9 hours vs 31.1 hours). A culture that was positive in </=18 hours was 13.0 (6.3-26. 6) times more likely to contain a pathogen than a contaminant. The average time from positive culture notification to reevaluation in the ED was 10.6 hours and over half of the patients recalled to the ED for positive cultures were admitted to the hospital. Of patients with occult pneumococcal bacteremia, 95.7% had resolution of their bacteremia without the use of parenteral antibiotics. Two patients had serious adverse outcomes. The rate of meningitis or death was. 03% (.004%-.12%). The contamination rate of blood cultures was 2.1% (1.7%-2.5%). Most (85%) of these patients were reevaluated in the ED and more than one third were admitted to the hospital before full identification of the organism.
CONCLUSIONS: Prevalence of occult bacteremia in the post-HIB vaccine era is lower than previously reported. S pneumoniae is the most common causative organism and resolves without parenteral antibiotics in the vast majority of cases. Continuously monitoring blood culture systems allow for early identification and can aid in differentiating contaminated from true pathogenic cultures by time to positive culture. Serious adverse outcome is an uncommon result of occult bacteremia. Updated epidemiology and microbiologic technology may impact the evaluation and treatment of children at risk for occult bacteremia.