Epidemiology of invasive meningococcal disease, Japan, 2013 to 2023.

BackgroundThe National Surveillance for Invasive Meningococcal Disease (IMD) initiative started in Japan in April 2013. Multiple international mass gathering events have since been held in Japan, and the COVID-19 pandemic has occurred.AimWe summarised 10 years of national surveillance data for IMD in Japan to describe epidemiological characteristics of IMD and evaluate the influence of mass gatherings and the COVID-19 pandemic on IMD.MethodsUpon diagnosis of IMD, patient information and specimens were collected and reported to local health centres. We analysed the epidemiology of IMD cases reported between 1 April 2013 and 31 March 2023.ResultsAmong 274 cases reported (median age: 55 years; 55% male), no outbreaks related to mass gathering events were identified. The annual reported incidence of IMD was 0.001-0.039 cases per 100,000 individuals between 2014 and 2022, with a notable decrease after 2020. The overall case fatality rate was 12% (33/274). The most frequent serogroups were Y and B (46 and 17%). Multilocus sequence typing revealed a predominance of clonal complex (cc) 23, followed by cc2057, while cc11 was detected in eight cases.ConclusionThe reported incidence of IMD in Japan is low compared with high-endemic countries and decreased further during the COVID-19 pandemic. This unique epidemiology of IMD in Japan lacks a clear explanation. However, distribution of meningococcal strains, such as predominance of serogroup Y, could be a contributing factor. Maintaining high-quality surveillance, including of serogroups and sequence types, is crucial to manage and prevent future IMD cases in Japan effectively.