Abstract
Background: In Japan, the number of HIV-1 infections remains relatively low; nevertheless, the annual incidence of HIV-1 infection has not decreased. New infections remain a great concern, and an improved understanding of epidemiological trends is critical for public health. Methods: The env C2V3 and pol sequences of HIV-1 RNA from 240 early (1996–2001) and 223 more recent (2010–2012) blood donations were used to compare the distribution of virus subtypes and to generate phylogenetic trees. Results: Subtype B was clearly predominant in both early and more recent donations (88.3% and 88.3%, respectively); CRF01_AE was the second-most-common subtype. Phylogenetic analysis revealed a peculiar epidemiological transition. Compared to early subtype B isolates from two major endemic areas (Tokyo and Osaka), the more recent subtype B isolates formed fewer tight clusters in phylogenetic trees (8 to 2 in Tokyo and 5 to zero in Osaka). Furthermore, mixing of HIV-1 infections between these two endemic areas seemed to have increased. Conclusions: Analysis of phylogenic trees suggested that the local outbreaks have become smaller in Japan; however, intermixing of viral types between these two areas was more evident in the more recent samples.
