Calculation of HIV infection rates and projection of the number of cases AIDS in Säo Paulo, Brazil using a backcalculation methods

RESUMO

Reconstruction of HIV infection rates and a projection of the number of AIDS cases in the City of Säo Paulo were determined using a backcalculation method. AIDS cases reported to the Centro de Vigilância Epidmiológica , the State Surveillance Departmen in Säo Paulo were adjusted for reporting delays through 1993 using a non-parametric delay distribution. The incubation period distribution was derived from a multicenter cohort study in the United States and modelled in two stages infection to CD4+ 200/mmü and CD4+ 200/mmü to AIDS diagnosis. After 1990, a factor reflecting the influence of treatment on the incubations distribution was used. Estimates were generated for the following risk cathegories homosexual/bisexual men, heterosexuals, and IV drug users (IDU). HIV infection rates peaked at approximately 10,000 new infections annually in the mid-1980s, followed by a tendency to stabilize around 4,000 new annual infections in the early 1990s. HIV infection curves varied among risk cathegories with a decrease in infections in homosexual and bisexual men, but a continuous rise in incidence rates estimated for heterosexuals. By projecting AIDS incidence rates a slight upward trend was seen with approximately 4,600 new cases expected in 1997. It is notable that over 4,400 cases would be expected in 1997, even if no new HIV infections occurred. Backcalculation methods are expected to be useful for evaluating changes in infection and disease in various risk groups, and the effects of therapy.