Influenza is a major cause of illness in children each year. Seizures and encephalopathy occur in 7-10% of children hospitalized with influenza; other neurologic complications have been reported but are poorly described. Our understanding of the overall incidence, risk factors and neuropathogenesis of all neurologic complications remains limited.

1. Define the epidemiology, risk factors, and characteristics of neurologic complications in a cohort of children hospitalized at a tertiary care pediatric hospital with laboratory-confirmed influenza.

Retrospective cohort study of children 0.5-18.0 years old hospitalized at a tertiary care pediatric hospital between 8/1/2010- 6/30/17 with laboratory-confirmed influenza. Eligible children were identified by electronic medical record query for influenza assay CPT codes with positive results during an admission in the study period; cases were confirmed by chart review. Demographics and clinical data were abstracted.

1258 children (mean 6.6 [SD 4.9] years) were hospitalized with laboratory-confirmed influenza during the study period. 10.3% percent (129/1258) had neurologic complications. While most neurologic complications were seizure (n=93) and encephalopathy (n=47), 19% (25/129) of children had other neurologic complications, including meningitis/encephalitis (n=7), ataxia (n=7), cerebral edema (n=4), movement disorder (n=3), arterial ischemic stroke (n=2), motor deficit (n=1), autonomic dysfunction (n=1), Bell’s palsy (n=1), PRES (n=1), and mutism (n=1). Median time between neurologic symptom onset and influenza test was 1 day. Children with neurologic complications were similar in age (6.1 vs 6.6 years, p=0.274) and had a similar distribution of influenza strains (H1, H3, B) compared to children without. Children with pre-existing neurologic diagnoses (668/1258) had a higher incidence of neurologic complications than those without (15% vs 5%, p<0.001), as did children with PICU admission (28% vs 6%, p<0.001).

Neurologic complications are common in children hospitalized with influenza. A better understanding of epidemiology and risk factors for these complications will direct future investigation into potential neuropathologic mechanisms and mitigating strategies.