• Morten Olsen, Sandra K Thygesen, John R Østergaard, Henrik Nielsen, Victor W Henderson, Vera Ehrenstein, Mette Nørgaard, and Henrik Toft Sørensen.
• Department of Clinical Epidemiology, Aarhus University Hospital, Aarhus N, Denmark.
• JAMA. 2015 Nov 3;314(17):1844-9.

ImportancePertussis is associated with encephalopathy and seizures in infants. However, the risk of childhood epilepsy following pertussis is unknown.ObjectiveTo examine whether pertussis is associated with the long-term risk of epilepsy.Design, Setting, And ParticipantsWe used individually linked data from population-based medical registries covering all Danish hospitals to identify a cohort of all patients with pertussis born between 1978 and 2011, followed up through 2011. We used the Civil Registration System to identify 10 individuals from the general population for each patient with pertussis, matched on sex and year of birth.ExposuresInpatient or hospital-based outpatient diagnosis of pertussis.Main Outcomes And MeasuresCumulative incidence and hazard ratio of time to hospital-based epilepsy diagnosis (pertussis cohort vs general population cohort), adjusted for birth year, sex, maternal history of epilepsy, presence of congenital malformations, and gestational age. Unique personal identifiers permitted unambiguous data linkage and complete follow-up for death, emigration, and hospital contacts.ResultsWe identified 4700 patients with pertussis (48% male), of whom 90 developed epilepsy during the follow-up. The cumulative incidence of epilepsy at age 10 years was 1.7% (95% CI, 1.4%-2.1%) for patients with pertussis and 0.9% (95% CI, 0.8%-1.0%) for the matched comparison cohort. The corresponding adjusted overall hazard ratio was 1.7 (95% CI, 1.3-2.1).Conclusions And RelevanceIn Denmark, risk of epilepsy was increased in children with hospital-diagnosed pertussis infections compared with the general population; however, the absolute risk was low.

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