Background: Antiretroviral therapy (ART) adherence predicts HIV disease progression and survival, but its effect on direct health care costs is unclear.
Objective: To determine the effect of ART adherence on direct health care costs among adults in a resource-limited setting.
Design: Cohort study.
Setting: Aid for AIDS, a private-sector disease management program in South Africa.
Patients: 6833 HIV-infected adults who started ART between 6 August 2000 and 30 April 2006.
Measurements: Monthly direct health care costs authorized by Aid for AIDS were averaged over all months. Pharmacy claim adherence, expressed as a percentage, was categorized into quartiles, from 1 (lowest) to 4 (highest). Effects of covariates on monthly total costs were assessed with a 2-step model with logit for probability of nonzero costs and a generalized linear model (GLM).
Results: Total mean monthly costs were $370 (SD, $644). Mean monthly costs of ART were $32 (SD, $18); hospitalizations, $151 (SD, $436); consultations, $76 (SD, $66); investigations, $37 (SD, $50); and non-ART medications, $53 (SD, $180). Total mean monthly costs ranged from $313 (SD, $598) for quartile 4 to $376 (SD, $657) for quartile 1. Hospitalization costs increased from 29% to 51% of total costs as adherence decreased. In the GLM 2-step model, moving from adherence quartile 1 to quartile 2, 3, or 4 increased the probability of having nonzero total monthly costs by 0.078, 0.15, and 0.21 percentage point, respectively (P < 0.001). For patients with nonzero costs, increasing adherence from quartile 1 to quartile 2, 3, or 4 decreased total monthly costs by $70, $133, and $192, respectively (P < 0.001). Moving from adherence quartiles 1 to 4 had the highest decrease in net overall median monthly health care costs (-$85 [interquartile range, -$116 to -$41]).
Limitations: Indirect health care costs were not included. Experience may not reflect that of public HIV/AIDS programs.
Conclusion: High ART adherence was associated with lower mean monthly direct health care costs, particularly reduced hospitalization costs, in this South African HIV cohort.