Hospital-Diagnosed Pertussis Infection in Children and Long-term Risk of Epilepsy.

IMPORTANCE Pertussis is associated with encephalopathy and seizures in infants. However, the risk of childhood epilepsy following pertussis is unknown. OBJECTIVE To examine whether pertussis is associated with the long-term risk of epilepsy. DESIGN, SETTING, AND PARTICIPANTS We 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. EXPOSURES Inpatient or hospital-based outpatient diagnosis of pertussis. MAIN OUTCOMES AND MEASURES Cumulative 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. RESULTS We 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 RELEVANCE In Denmark, risk of epilepsy was increased in children with hospital-diagnosed pertussis infections compared with the general population; however, the absolute risk was low.