When to Start HIV Treatment: Evidence from a Regression Discontinuity Study in South Africa

Jacob Bor, Boston University
Ellen Moscoe, Harvard University

To date no experimental or quasi-experimental evidence exists on the survival impact of early vs. delayed antiretroviral therapy (ART) for HIV in sub-Saharan Africa. We estimate causal effects using a regression-discontinuity design. Like many clinical therapies, ART is assigned based on a threshold rule, with eligibility determined by a patient’s CD4+ count being below a threshold. We analyzed data on 4391 HIV patients from a demographic surveillance in rural South Africa. Patients presenting for care with a CD4+ count just below 200 cells/µL were 4.3% points (95%CI 0.6,8.0) more likely to be alive at two years than patients with CD4+ just above 200; effects persisted at five years. These effects imply a 14.9% point two-year survival advantage for patients who actually initiated ART because they were eligible. Large gains in immune function were also observed. Additional medical care provided to ART-eligible patients implied a cost of $1967 per life-year saved.