The changing incidence of AIDS events in patients receiving highly active antiretroviral therapy

BACKGROUND: Although the incidence of most AIDS events declines after initiation of highly active antiretroviral therapy (HAART), this decline is more rapid for some conditions than others. We herein describe the decline in incidence of AIDS-defining events among 12,574 antiretroviral-naive individuals who started HAART in the Antiretorviral Therapy Cohort Collaboration and determined whether the rate of decline is similar for events with different etiologies. METHODS: Rates of AIDS were calculated for the periods 0 to 3, 4 to 6, 7 to 12, 13 to 24, and 25 to 36 months after starting HAART. Changes in incidence over time were investigated using Poisson regression. RESULTS: During 22 958 person-years of follow-up, 928 AIDS events developed (25.3% viral, 24.6% bacterial, 20.7% fungal, 8.1% protozoal, and 21.2% other). The incidence of any AIDS event declined from 129.3 (95% confidence interval [CI], 116.7-141.8) per 1000 person-years in the first 3 months to 13.2 (95% CI, 9.4-17.0) in the third year after starting HAART (P[Lt].001). The rate of decline in incidence was greatest for events with a viral etiology (87.0% per year) and lowest for those with a fungal etiology (54.0% per year). In the third year, fungal events represented 37.0% of AIDS events that occurred. After adjustment for the CD4 count and human immunodeficiency virus 1 RNA level, changes in the incidence of bacterial and viral events from months 0 to 6 and 7 to 12 remained significant, suggesting that changes in these markers did not fully explain the changes in incidence seen. CONCLUSION: Although the incidence of all AIDS-defining events decreased substantially after starting HAART, the pattern of decline was most pronounced for events with a viral etiology.