Secular Trends in the Incidence of Encephalitis and Outcomes of Postencephalitic Epilepsy in Taiwan: A Nationwide Population-Based Study

Background: Encephalitis can lead to significant disability among survivors. Up-to-date estimates of encephalitis incidence and the risk of postencephalitic epilepsy (PE) are crucial for informing health policy. Methods: We used the National Taiwan Insurance Research Database to estimate the standardized incidence of encephalitis for each year from 2003 to 2017. We analyzed PE among these cases. Results: From 2003 to 2017, the age- and sex-standardized incidence of encephalitis increased from 5.95 (95% confidence interval [CI]: 5.61–6.28) to 10.46 (95% CI: 10.04–10.87) per 100, 000 person-years, with an annual percentage change of 1.6% (1.1–2.2, p < 0.05). However, yearly variation was observed. The incidence was consistently higher in patients under 18 years than in those aged ≥ 18 years throughout the study period. In 2017, the highest annual incidence was seen in adults aged ≥ 70 years and in children aged 1–4 years. Approximately 20% of the survivors developed PE within 5 years, with the highest risk observed in infants under 1 year of age. Conclusion: The overall incidence of encephalitis in Taiwan increased from 2003 to 2017. Pediatric patients, particularly those under 1 year of age, are more vulnerable to encephalitis and its long-term complications, including PE, compared to adults, except for those aged ≥ 70 years.