Temporal changes in the rate of progression to death among Italians with known date of HIV seroconversion: estimates of the population effect of treatment. Italian HIV Seroconversion Study (ISS).

OBJECTIVE: To evaluate changes in survival among HIV-positive individuals with known date of seroconversion (SC).
DESIGN: Prospective cohort study.
METHODS: Follow-up lasted from SC to death or to the end of 1997. A multivariate Cox model was applied to estimate relative hazards (RH) of death. The year of SC (as a categoric fixed variable) and calendar year (as a time-dependent variable) were considered to evaluate, respectively, cohort and prevalent changes in the rate of death. A separate Cox model was used to assess the association between survival and new combination therapies, using an "intention to treat" approach.
RESULTS: The study included 1535 individuals (53.9% injecting drug users, 25.3% homosexuals, 19.5% heterosexuals); 75.8% seroconverted between 1980 and 1991, and 24.2% seroconverted between 1992 and 1997. When adjusting for year of SC, the RH of death (and that of AIDS) was significantly lower in 1997, compared with before 1991 (RH = 0.54; 95% confidence interval, 0.30-0.98). Adjusted RHs of death were significantly lower for combination antiretroviral therapy, compared with no therapy. When combining the two Cox models, the 1997 reduction in risk of death was largely due to antiretroviral therapies; similar results were obtained when the endpoint was AIDS.
CONCLUSIONS: A reduction in the risk of death, probably due to combination antiretroviral therapy, was observed in 1997 after having adjusted for age at SC and year of SC.