Objective: To describe the rate of new AIDS events over the first year of HAART in patients with different characteristics and to describe the decrease in incidence of AIDS between the first and second 6 months of the year in these patients.
Design: Collaboration of cohort studies from Europe and North America.
Methods: AIDS rates in the first year of HAART were calculated for 22 217 antiretroviral-naive individuals. Event rates were compared in the periods 0-6 and 7-12 months after starting HAART.
Results: The number of events and person-years of follow-up (PYFU) in the two time periods were 1185 (9601) and 336 (8690), respectively (event rates: 12.3 and 3.9 per 100 PYFU, relative decline in incidence: 68%). Whereas rates decreased in all groups, tests for interaction suggested that relative declines in incidence were more rapid in homosexual men (P = 0.002), in those starting HAART from 2001 in comparison with earlier years (P = 0.03), in those with lower CD4 cell counts (P-values of 0.001, 0.002 and 0.11 for those with cell counts < 50, 50-199 and 200-349 cells/microl compared to those with cell counts >or= 350 cells/microl) and HIV RNA levels >or= 5 log10 copies/ml (P = 0.0008). Those with AIDS at the time of starting HAART had a less rapid relative decline in incidence (P = 0.0007).
Conclusions: Our results suggest that some groups may experience less rapid relative declines in AIDS incidence than others over the first year on HAART.