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.
(© 2022. Japanese Society of Gastroenterology.)