P3.F107: Incidence of Influenza-Associated Serious Neurologic Events in Young Children

Background: The American Academy of Pediatrics and the Infectious Diseases Society of America recognize children < 5 years of age and those with neurologic conditions to be an at-risk population for complications of influenza such as hospitalization and death. The incidence of serious influenza-associated neurologic events in U.S. children < 5 years of age is unknown. The objective of this study was to determine the population-based incidence of influenza-associated serious neurologic events in children < 5 years of age.

Methods: Children < 5 years with an outpatient ICD-10 diagnosis of influenza during the 2016/2017-2019/2020 influenza seasons were identified using the Tennessee Medicaid database. To reduce misclassification of influenza infections, each influenza season was defined as the 13 consecutive weeks including the maximum number of laboratory-confirmed influenza cases in Tennessee. Serious influenza-associated neurologic events were defined as a neurologic event resulting in hospitalization and identified using an algorithm previously validated in children age 5-17. Follow-up for outcome ascertainment began on the date of the influenza diagnosis and continued for a total of 10 days unless on of the following occurred: end of influenza season, loss of enrollment, death, or occurrence of a qualifying serious neurologic event. The crude incidence of serious influenza-associated neurologic events was calculated by dividing the number of events by the total influenza person-time and expressed per 100,000 person-weeks of influenza. Estimates were stratified by age, sex, neurologic comorbidity, influenza season, and antiviral use.

Results: A total of 79,727 cases of influenza among 70,258 unique children < 5 years were included. 65% of children were > or equal to 2 years of age, 48% were female, 2% had complex chronic conditions and 0.4% of the children had an underlying neurologic comorbidity; 63% of children received antiviral treatment. Demographic information is shown in Table 1. The overall incidence of serious influenza-associated neurologic events in children < 5 years of age was 40.6 (95% CI 29.8-54.2) per 100,000 person-weeks of influenza. Incidence rates were similar when stratified by age, sex and antiviral treatment (Figure 1). Incidence was ~100-fold higher in those with underlying neurologic conditions compared to those without. Seizures were the most common neurologic event (34.4, 95% CI 24.5-47.1) and encephalitis was rare (0.9, 95% CI 0.02-4.9).

Conclusion: In this large retrospective cohort study, we determined the incidence of serious influenza-associated neurologic events in children < 5 years and showed that the incidence is markedly increased in children with underlying neurologic conditions. These findings emphasize the importance of mitigating influenza through prevention and vaccination efforts to prevent serious influenza complications, especially among young children with an underlying neurologic comorbidity.