New therapy explains the fall in AIDS incidence with a substantial rise innumber of persons on treatment expected

Background: A marked decline in the number of reported AIDS cases has been observed in the United Kingdom, as in many industrialized countries, in 199 6 and 1997. In England and Wales, a large reduction in AIDS cases has been recorded among homosexual and bisexual men. Objectives: To investigate, using data from the homosexuals and bisexuals i n England and Wales as an example, possible explanations for the above decl ine such as the effects of new anti-retroviral therapies, or a decrease in the incidence of HIV in recent years. Methods: A multistage model of HIV infection, HIV diagnosis, treatment and of AIDS diagnosis has been used to represent the pattern of HIV and AIDS in cidence in homosexual and bisexual men in England and Wales up to the end o f 1995. Scenarios for the post-1995 period were examined under different as sumptions about changes in HIV incidence in recent years and treatment upta ke and efficacy. Results: The fall in the incidence of AIDS is unlikely to be the result of a reduction in HIV transmission during the 1990s. The most plausible explan ation for this fall is the effect of new, more effective, anti-retroviral t herapies. As a consequence, the number of individuals on treatment is likel y to increase by 50 to 100% compared with the pre-1996 revels by the year 2 001. Also, if the effect of the new therapies has a limited duration, or th e use of such therapies is not well tolerated, the incidence of AIDS will r ise again in the near future. Conclusions: These findings indicate that a substantial workload increase i s under way for the healthcare system, and reiterate the need for measures to reduce HIV transmission as a means of bringing about a sustainable chang e in the incidence of AIDS. (C) 1999 Lippincott Williams & Wilkins.