HIV/AIDS in Japan: Route and Age of Infection that Shaped the Epidemics in 1987-2016.

In Japan, HIV infection is classified as "HIV" or "AIDS" depending upon whether the infection was detected before or after the development of AIDS. In male homosexuals, in the plot of the number of "AIDS" notified annually versus the that of "HIV" notified annually, the plot fell on a straight line with a slope close to 1. When the number of "HIV" no longer increased, that of "AIDS" also stopped increasing. The number of "HIV" notified in one region or age group was correlated with that of other regions or age groups, respectively. However, no such correlation was observed among male heterosexuals. "HIV" was detected more frequently among male homosexuals and females than among male heterosexuals. The rate of "AIDS" detection increased with age in all infection categories. Our analysis, supported by findings of other studies, suggested that the higher rate of "HIV" detection among male homosexuals and females was attributed to the increased risk of receptive sexual intercourse, while the higher rate of "AIDS" detection among the elderly people was attributed to immunological senescence.