(A31) Population-Based Incidence of Influenza-Associated Serious Neuropsychiatric Events

Publication Number: 314

Background: While influenza is known to cause life-threatening neuropsychiatric symptoms (e.g., psychosis, seizures, suicidal or homicidal ideation), the incidence of influenza-associated neuropsychiatric events is unknown. The lack of an established baseline incidence rate has limited efforts to determine whether the influenza antiviral oseltamivir is also associated with neuropsychiatric events as reported on the manufacturer label.

Objectives: To determine the population-based incidence of influenza-associated serious neuropsychiatric events

Methods:

Methods: We assembled a retrospective cohort of children (5-17 years) enrolled in Tennessee (TN) Medicaid with an outpatient ICD-10 diagnosis of influenza during the 2016-2020 influenza seasons. To maximize accuracy of influenza diagnosis, each season was restricted to the 13 consecutive weeks with the highest influenza incidence in TN based on CDC Surveillance data. The study outcome was an influenza-associated serious neuropsychiatric event, defined as a neuropsychiatric event resulting in hospitalization within 10 days of an influenza diagnosis and was identified using a validated algorithm (PPV~90%). Individuals were censored at the time of: loss of enrolment, hospitalization, or death. Incidence was calculated by dividing the total number of influenza-associated serious neuropsychiatric events by the total number of eligible person-days of influenza and reported as person-weeks of influenza. Incidence was calculated overall and by age, sex, presence of a neuropsychiatric co-morbidity, presence of a risk factor for influenza complications, presence of antiviral dispensing, and influenza season.

Results: A total of 156,661 individuals with influenza were included. Median age was 9.3 years (IQR 6.9, 12.6). The overall incidence of influenza-associated serious neuropsychiatric events was 50.7 (95% CI 41.1, 60.9) per 100,000 person-weeks of influenza. The most common neuropsychiatric events were seizures and mood disorders (both 17.5, 95% CI 12.8, 24.0), and the least common was encephalitis (0.5, 95% CI 0.02, 2.6). Incidence of suicidal and self-harm events were 0.9 (95% CI 0.3. 3.3). Incidence rates were highest in those with: neurologic conditions, psychiatric disorders, risk factor for influenza complications, and older children. Incidence among oseltamivir exposed (51.6, 95% CI 41.3, 64.5) and unexposed (49.1, 95% CI 41.2, 65.0) were similar.

Conclusions: The incidence of influenza-associated serious neuropsychiatric events is low in the pediatric population but varies significantly based on age, co-morbid conditions, and other factors. Additional study is needed to evaluate whether immunization or oseltamivir use modifies the risk of these events.