Trends of hepatitis B virus genotype distribution in chronic hepatitis B patients in Japan

Background Hepatitis B virus (HBV) is one of the most prevalent chronic viral infections that causes chronic hepatitis B (CHB). In Japan, genotypes B and C account for most of acute and chronic cases of hepatitis. However, previous studies showed that the prevalence of genotype A in CHB gradually increased every 5 years. Therefore, we have conducted a nationwide survey to comprehensively investigate the trends of HBV genotype distribution in CHB patients in Japan. Methods 4421 CHB patients were recruited between 2015 and 2016. Clinical characteristics and distribution of CHB patients among different age groups and genotypes in 2015-2016 was compared with those in 2000-2001, 2005-2006, and 2010-2011. Results The percentages of genotype A, B, C, and D were 4.0, 16.2, 79.1, and 0.7%, respectively. While the overall percentage of CHB patients with genotype A did not change in the past 5 years, CHB with genotype A increased in young adults. On the other hand, the peak distribution of CHB with genotypes B and C, two genotypes with the largest patient population, has shifted to an older age group. Conclusions In Japan, the peak distribution for CHB with genotypes B and C advanced to an older age group while CHB with genotype A expanded in a younger age group. Given the universal HBV vaccination launch in Japan in 2016, these pre-vaccination survey data provide important baseline information for comparative studies of the impact of universal vaccination on HBV genotypes.