Seroepidemiology of hepatitis A virus infection in Japan: An area of very low endemicity.

The incidence of hepatitis A virus (HAV) infection has declined significantly worldwide, including in Japan. A nationwide seroepidemiological study on hepatitis A in Japan has taken place almost every 10 years since 1973, and the last study was performed in 2003. In the present study, we describe the latest seroepidemiological pattern of hepatitis A in Japan using 7867 serum specimens obtained from healthy individuals collected between 2013 and 2017, approximately 10 years after the last study. Among them, 223 were anti-HAV positive. About 68% of individuals aged 60 years and older had anti-HAV antibodies, whereas only 1.1% of those aged below 60 years old had immunity; thus, almost all individuals younger than 60 years of age were HAV susceptible. In comparison with previous investigations, the susceptible population has increased and aged. According to data from the National Epidemiological Surveillance of Infectious Diseases (NESID) program, between 1989 and 2016, the proportion of patients with hepatitis A aged 60 years and older continuously increased with each year. The NESID data also suggested that recently, typical large foodborne outbreaks of hepatitis A have become rare, and cases tend to be reported among at-risk groups; overseas travelers contributed to 25% of hepatitis A cases, and in 2018, the first nationwide hepatitis A outbreak that affected mostly men who have sex with men was reported. The purpose of this study was to determine the current status of HAV infection in Japan, based on both seroepidemiology and the national surveillance data from the NESID.