I’m in Nagasaki this week to attend the 86th Annual Meeting of the Japanese Society for Infectious Diseases, where I have presented the results of my work building a mathematical model of the HIV Epidemic in Japan. The model is currently submitted to a journal so I can’t give any detail about it here, but I can present a chart I used in the conference presentation, that is based on publicly available data from the Ministry of Health, Labour and Welfare. This chart shows the number of new cases of HIV/AIDS notified to the government annually, divided into three main transmission modes (Figure 1).

Figure 1: Annual new cases of HIV/AIDS in Japan by transmission category, 1985-2010

In this Figure, “same sex contact” means “homosexual contact,” since there’s no such thing as a case of HIV transmitted by same sex contact between women. From Figure 1 it should be pretty clear that while the epidemic appears to have peaked and even beginning to decline in the heterosexual population, amongst men who have sex with men (MSM) it is growing rapidly. Now, there are some caveats on such a conclusion in Japan: testing rates are quite low so it could be that these “new” cases are actually old cases that have only just been identified, for example, but it would be a strange world indeed if the entire slope of that line were due to remnant cases finally coming to light. So, it’s reasonable to conclude with some confidence that the HIV epidemic is growing rapidly amongst MSM in Japan. Currently prevalence is probably low, but that was the case in Australia back in 1985, and prevalence amongst MSM in Australia now is probably above 5%.

This comparison is noteworthy because Figure 1 makes it look like Japan’s experience of HIV is Australia’s 20 years ago, and if the epidemic continues to follow Australia’s trend, HIV will spread rapidly through Japan’s gay community. Of course there are big differences in HIV treatment and prevention now compared to 20 years ago, and very few people die of AIDS in Japan because of the combination of low prevalence and good treatment. But the rapid increase amongst MSM shown in Figure 1 suggests that prevention efforts to date haven’t been working, and it would be best if something could be done to prevent the further spread of the disease.

Another minor concern (raised in my presentation, actually) is that MSM in Japan tend to be less open than in the rest of the developed world, making them even harder to study but also raising the possibility that they marry and have at least some sexual contact with women. Sexuality in Asia is, in general, more fluid than in the West and less constrained by categories and boundaries, so the idea seems superficially plausible. If this is true though, it means that there is a small risk that the epidemic won’t be contained within the gay community forever. Unfortunately, no one knows the extent of this overlap in Japan, and no one knows how much injecting drug use is happening here, so it’s hard to make judgments about how such behavior might affect the future of the epidemic. This is what my mathematical modeling is (partially) aiming to do, and although I won’t reveal the results here the future is not pretty for MSM if the epidemic is allowed to continue. Even without the benefit of a mathematical model, it’s pretty easy to see from Figure 1 that Japan needs to improve interventions amongst MSM, primarily by increasing rates of voluntary testing and targeting a test-and-treat prevention strategy at this community. Given the current low prevalence of HIV, even a relatively unsuccessful test-and-treat program will probably be sufficient to contain the epidemic (though the international evidence suggests that it takes a very rigorous and probably unrealistically well implemented program to eliminate the disease). It remains to be seen whether such a targeted approach will be tried here, but hopefully my work will be one tiny step towards encouraging such a change.

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