[Molecular Epidemiological Analysis of Hepatitis A Viruses Circulating in Tokyo, 2016-2017]

Hepatitis A virus (HAV) is a common infectious agent that causes acute hepatitis worldwide. Since the incubation period of HAV infection is about one month, it is difficult to identify the source of infection based only on medical interviews. Molecular epidemiological analysis of HAV isolated from patients can help to reveal the infection route and to identify diffuse outbreaks caused by common food vehicles. In the present study, samples were collected from 108 cases notified to the active epidemiological investigation system in Tokyo between 2016 and 2017. Samples found to be HAV-positive by semi-nested RT-PCR were subjected to sequencing and phylogenetic analysis; the results were analyzed together with the epidemiological data. HAV was detected in 99 out of 108 cases. Phylogenetic analysis showed that the 99 HAV strains were divided into 91 of genotype IA, two of IB, and six of IIIA. The 91 HAV strains typed as IA were further divided into four main line-ages, IA-1, IA-2, IA-3, and IA-4, each with a unique epidemiological background. Our nucleotide sequence database of HAV and epidemiological background data will be helpful to investigate sources of infection and the epidemiology of hepatitis A cases in the future.