96 - Invasive bacterial infection rates increase with advancing age in healthy, full term febrile infants aged 8-56 days: a population-level analysis

Poster Number: 96
Publication Number: 96.1386

Background: Prior studies suggest that invasive bacterial infection (IBI; i.e., bacteremia and bacterial meningitis) risk progressively declines with age among febrile infants aged 8-56 days. However, estimates rely upon hospital data and may be limited by selection bias related to caregivers’ decisions to seek care for an infant with fever. To address this limitation, a population-level sample, that is not contingent on care-seeking behavior, is needed.

Objective: Thus, the objective of this study was to estimate population-based week-by-week IBI rates among febrile infants aged 8-56 days and to compare findings with hospital-based week-by-week IBI rates.

Design/Methods: We used New York State’s comprehensive, all-payer database to create a retrospective cohort of febrile infants brought to emergency departments in New York State from January 2012-December 2022. Inclusion criteria were age 8-56 days, full term birth (>37 weeks gestational age at birth), no complex medical condition, and encounter in an emergency department for fever. We excluded infants transferred from other facilities. We used published diagnosis codes to identify infants with fever and infants with the main outcome of IBI. We calculated total IBI, bacteremia and meningitis rates among febrile infants per 10,000 healthy, full-term, live births for every week of life (i.e., 8-14 days, 15-21 days, etc.). We then repeated the analysis for hospital-based week-by-week rates using the total number of febrile infants for every week of life as the denominator and compared findings.

Results: Of >2.1 million live births to full term infants without complex medical conditions, 37,159 febrile infants met inclusion criteria with >1,300 total IBIs (Table 1). For the population-based analysis, we observed increasing rates of bacteremia and total IBIs, and declining rates of bacterial meningitis with increasing age in weeks (Figure 1). For the hospital-based analysis, although some total IBI and bacteremia risk estimates were greater in the 2nd month of life compared with the 1st month, we observed progressively declining total IBI, bacteremia and meningitis rates by week of life (Figure 2).

Conclusion(s): This population-based analysis demonstrates that IBI risk increases with advancing age during the first 2 months of life for febrile infants in contrast to the hospital-based analysis. Future studies should seek to understand this relationship to improve the accuracy of IBI risk estimates for febrile infants.