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In December 1995 and March 1996, we visited institutes which were conducting epidemiological studied of HIV/AIDS in Cambodia, and obtained data for further collaborative study between Japan and Cambodia. Data included information on AIDS patients and HIV infected persons, and behavioral epidemiology of CSWs (Commercial Sex Workers). The cumulative reported number of AIDS patients and HIV infected persons in Cambodia was 86 and 2,536 cases respectively in 1995. The cause of infection was mostly heterosexual contact with very few cases from injecting drug use (IDU) and other causes. The seroprevalence rate of HIV antibody among donated blood rapidly increased from 0.08% in 1991 to 4.47% in 1995, and those among CSWs and pregnant women were 37.9% and 2.6%, respectively, in 1995. The average rate of condom use among CSWs was 66%, but the rate of usual usage was only 14%. These results indicate that the HIV/AIDS epidemic had spread rapidly through CSWs, that it had been spread among peoples in communities, and that usage of condoms among CSWs was insufficient in Cambodia. Without strong countermeasures against HIV/AIDS in this country, HIV/AIDS epidemic may spread significantly to not only peoples in this country but also those in neighbouring countries in the future.

The data obtained from the national reporting system of acquired immune deficiency syndrome (AIDS) and its causative immune deficiency virus (HIV), the epidemic pattern of AIDS cases and HIV carriers in Japan from 1985 to 1995 could be summarized as follows: 1) the total number of reported AIDS cases and HIV carriers were 1,154 and 3,524 which included 167 and 915 foreigners, respectively; 2) among them the number of HIV carriers in hemophiliacs transmitted through HIV contaminated blood products was 1,806, including 582 AIDS victims; 3) excluding these hemophiliacs, there are 572 AIDS cases (167 foreigners) which shared risk factors for heterosexual contacts (37%) and homosexual contacts (31%), respectively; 4) on the other hand, more than 50% were heterosexuals and only 20% were homosexuals in 1,718 HIV carriers (915 foreigners); 5) the peak incidence is 33% in the 30s in AIDS, while more than 50% are in their 20s; 6) male-to-female ratio was 6.8 in AIDS cases but only 1.1 in HIV carriers; 7) the estimated number of HIV carriers in 2000 was 6,300-8,500 in Japanese and 700-1,700 in foreigners, respectively. From the above mentioned epidemic pattern of AIDS/HIV in Japan, we have to recognize that the recent number of HIV infection is actually increasing and the most of current HIV carriers even in foreigners are infected with HIV in our country and general activities for AIDS prevention in Japan and neighboring Asian countries should be promoted.

HIV/AIDS surveillance in Japan experienced a sharp and transient rise in 1991-92 in the number of foreign HIV positives but not of AIDS cases, for reasons of which remain unclear. Using the national HIV/AIDS surveillance data base the cause of the increase was studied by comparing the trends of foreign cases diagnosed in 1991-92 with those in 1985-90 in terms of gender, age, nationality, clinical stage, possible route of infection, possible place where the case contracted HIV and the place where the case was identified. Present analysis revealed: (1) In 1991-92 there was a large increase in the number of heterosexually-infected female HIV positive aged below 30 years reported from the areas surrounding Tokyo, of which the majority was of Asia origin. (2) A similar but moderate change was also seen in foreign males infected heterosexually but not in those infected homosexually. These were predominantly of U.S./Europe origin, aged > or = 30 and reported from Tokyo. (3) Although most of the foreign cases reportedly contracted HIV outside of Japan, those infected in Japan began being reported in 1991-1992. These results suggest that change in foreign cases seen in 1991-1992 was not only in number but also in gender, age, nationality, route of infection and geographical distribution. This should be taken into consideration in considering the HIV/AIDS prevention strategy in Japan.

Current status and future trends of HIV infection and AIDS in Japan were estimated based on AIDS surveillance data up until 1992, excluding HIV infection from blood products and blood-borne transmission. The coverage rate of reports of HIV infection was estimated as the proportion of the reported AIDS cases who are also included in reports of HIV infection. Current numbers of HIV infected persons were then estimated to be the reported numbers divided by the coverage rate. Future numbers of HIV infected persons were predicted by extrapolation. Future numbers of AIDS cases were predicted based on the predicted numbers of HIV infected persons and the incubation distribution. The results were as follows: 1) The coverage rate of the reports of HIV infection was estimated to be 11.5%. 2) The numbers of HIV infected persons were estimated to be 2,900 in Japanese and 4,500 in foreigners by the end of 1992, and are predicted to be 7,700 in Japanese and 15,500 in foreigners by the end of 1997. 3) The numbers of AIDS cases were reported to be 125 in Japanese and 52 in foreigners by the end of 1992, and are predicted to be 1,100 in Japanese and 1,600 in foreigners (including AIDS cases developed after return to home country) by the end of 1997.

In Japan, the AIDS (Acquired Immunodeficiency Syndrome) epidemic among haemophiliacs has been the most urgent issue, because of the large number of haemophiliacs with AIDS. However, after governmental approval of the production of heated coagulating agents in 1985 and 1986, the prime object of prevention against the AIDS epidemic shifted from transmission through coagulation agents to that through sexual contacts. In order to investigate the most appropriate countermeasures against the AIDS epidemic among homosexuals in Japan, the numbers of HIV (Human Immunodeficiency Virus)-infected cases and AIDS cases in the future were estimated, and changes of the future numbers of HIV-infected persons and AIDS cases by behavior of homosexuals were compared using a systems analytical method. The methods of estimation and comparison are similar to those of R. M. Anderson and others, using numerical analysis of a mathematical model consisting of differential equations. They assumed a closed homosexual group whose members seldom have contact with members of other homosexual groups, but we assumed an open homosexual group whose members are being infected by other groups, because this assumption was more appropriate to the situation of homosexual society in Japan. The results showed that the prevalence number of HIV-infected cases would be about 1,800, that the prevalence number of AIDS cases would be about 100 among 100,000 homosexuals at 20 years after the beginning of the AIDS epidemic, and that the most effective countermeasure was reducing the frequency of sexual contacts among members or taking prophylactic measures during sexual contacts. These prevalence numbers of HIV-infected cases and AIDS cases would be reduced to between 1/4 and 1/2 of the above-mentioned calculated values by promotion of that countermeasure.