Background. In recent years a decline in the number of new AIDS cases has been observed in several industrialized countries. It is important to know whether these recent trends observed in North America and Europe are also occurring in Japan. Methods. The number of people reported with HIV and AIDS by nationality, route of infection, and sex was calculated based on the HIV/AIDS surveillance data available in Japan through December 1997. The effect of reporting delay, which was defined as those HIV and AIDS cases reported in the calendar year following diagnosis, on the trends was examined. The coverage rate in reporting HIV cases was estimated as the ratio of the reported AIDS cases with prior report as an HIV-positive to the total number of reported AIDS cases. Results. The cumulative number of reported cases of HIV among Japanese and non-Japanese residents of Japan up to the end of 1997 were 1300 and 1190, respectively. The cumulative number of reported cases of AIDS among Japanese and non-Japanese up to the end of 1997 were 758 and 298, respectively. The number of reported cases of HIV among Japanese was found to be still increasing, with the major contribution from male cases. The increasing trend in the number of reported AIDS cases among Japanese began to slow in 1996 and 1997. The number of reported cases of HIV among non-Japanese residents of Japan peaked in 1992, and has decreased since then, and remained constant after 1994. In contrast, the number of reported AIDS cases among these non-Japanese tended to increase gradually. There was a slight reporting delay for people with HIV and AIDS. The estimated coverage rate in reporting HIV cases tended to decrease in 1996 and 1997 (1/7.2, 1/10.2, respectively). We point out several reasons for this recent decline and suggest the possibility of an ostensible decline in the estimates. Conclusions. We suggest that the number of people with HIV among Japanese has continued to increase, and that the increase in the number of AIDS cases among Japanese is now slowing.
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