Childhood seizures after prenatal exposure to maternal influenza infection: a population-based cohort study from Norway, Australia and Canada.

Objective To assess whether clinical and/or laboratory-confirmed diagnosis of maternal influenza during pregnancy increases the risk of seizures in early childhood. Design Analysis of prospectively collected registry data for children born between 2009 and 2013 in three high-income countries. We used Cox regression to estimate country-level adjusted HRs (aHRs); fixed-effects meta-analyses were used to pool adjusted estimates. Setting Population-based. Participants 1 360 629 children born between 1 January 2009 and 31 December 2013 in Norway, Australia (New South Wales) and Canada (Ontario). Exposure Clinical and/or laboratory-confirmed diagnosis of maternal influenza infection during pregnancy. Main outcome measures We extracted data on recorded seizure diagnosis in secondary/specialist healthcare between birth and up to 7 years of age; additional analyses were performed for the specific seizure outcomes ‘epilepsy’ and ‘febrile seizures’. Results Among 1 360 629 children in the study population, 14 280 (1.0%) were exposed to maternal influenza in utero. Exposed children were at increased risk of seizures (aHR 1.17, 95% CI 1.07 to 1.28), and also febrile seizures (aHR 1.20, 95% CI 1.07 to 1.34). There was no strong evidence of an increased risk of epilepsy (aHR 1.07, 95% CI 0.81 to 1.41). Risk estimates for seizures were higher after influenza infection during the second and third trimester than for first trimester. Conclusions In this large international study, prenatal exposure to influenza infection was associated with increased risk of childhood seizures.