Methods to assess population effectiveness of therapies in human immunodeficiency virus incident and prevalent cohorts

Two methods are presented for measuring population effectiveness (i.e., red uction of disease in a population in which only some receive treatment) of antiretroviral therapy among human immunodeficiency virus (HIV)infected men at risk for acquired immunodeficiency syndrome (AIDS) and followed between January 1, 1986, and June 30, 1999, in the Multicenter AIDS Cohort Study. Method I, requiring use of a seroincident cohort, estimates relative hazard s of AIDS for persons at equal duration of infection. Method II, allowing u se of a seroprevalent cohort, estimates relative hazards since the beginnin g of therapy eras for persons starting at equal levels of prognostic marker s of disease stage (CD4 cell count and HIV type 1 RNA). The follow-up inter val was divided into four calendar periods to characterize different eras o f antiretroviral therapy. For method I, the relative hazards were 1.52 (95% confidence interval (CI): 0.93, 2.49), 0.91 (95% CI: 0.66, 1.26), and 0.30 (95% CI: 0.18, 0.51) for the eras of no therapy, dual nucleoside therapy, and potent combination antiretroviral therapy, respectively (monotherapy wa s the reference era). For method II, the corresponding relative hazards wer e 1.52 (95% Cl: 1.10, 2.09), 1.03 (95% CI: 0.77, 1.38), and 0.31 (95% CI: 0 .21, 0.45). These results extend the measurement of population effectivenes s from incident to prevalent cohorts and demonstrate the ability of cohort studies to complement information provided by clinical trials.