Acute Encephalitis/Encephalopathy Associated With Infectious Diseases in Fukushima Prefecture, Japan: An Epidemiologic Study

BACKGROUND: Multiple epidemiologic surveys of acute encephalitis/encephalopathy have been conducted in Japan; however, information on incidence rates and related infectious diseases/pathogens remains limited. OBJECTIVE: To clarify the epidemiological characteristics of acute encephalitis/encephalopathy in Fukushima Prefecture, we investigated the number of cases and the associated infectious diseases/pathogens using polymerase chain reaction (PCR) in addition to conventional diagnostic methods. METHODS: We collected data on acute encephalitis/encephalopathy cases from 16 medical institutions in Fukushima Prefecture that provided pediatric inpatient care between 2014 and 2024. At Fukushima Medical University Hospital, PCR testing was used in addition to conventional diagnostic methods to identify the related pathogens. RESULTS: Over the 11-year study period, 106 cases of acute encephalitis/encephalopathy associated with infectious disease were reported, with an average of 9.6 cases per year and an annual incidence rate of 15.2 per 100,000 children aged under 5 years. Associated infectious diseases/pathogens were identified in 59.4% of cases: exanthema subitum/human herpes virus-6,7 in 22.6%, influenza/influenza virus in 18.9% and other in 17.9%. Among 50 cases admitted to Fukushima Medical University Hospital, the pathogen identification rate was 76.0%: human herpes virus-6,7 in 24.0%, influenza virus in 22.0% and other pathogens in 30.0%. CONCLUSION: Based on the prospective active survey of acute encephalitis/encephalopathy in Fukushima Prefecture, the annual incidence rate is estimated to be 15.2 cases per 100,000 children under the age of 5 in Japan. Since PCR testing is effective for detecting pathogens, comprehensive PCR analysis may further improve pathogen identification in acute encephalitis/encephalopathy.