Preventive therapy for tuberculosis in HIV-infected persons: Analysis of policy options based on tuberculin status and CD4+cell count

Background: To facilitate decisions about the possible implementation of isoniazid preventive therapy (IPT) for human immunodeficiency virus (HIV)- infected persons on a large scale, the benefits and associated costs of various policy options of IPT should be evaluated. Methods: Variable values based mainly on a prospective cohort study performed in Italy were used in an epidemiological model to assess the effects of the administration of IPT to the following groups of HIV-infected individuals: (1) tuberculin positive; (2) anergic, with various levels of immunosuppression; and (3) all HIV- infected individuals. The calculations of the costs associated with each policy option were based on the situation within the Italian national health care system. Outcome measures were average cohort survival times, total quality-adjusted life years lived in the cohort, total economic costs, and marginal costs per marginal quality-adjusted life year saved for each policy option. Results: Median life expectancy gains from IPT were 104 to 149 days for tuberculin-positive individuals and 19 to 27 days for anergic patients. The largest gains were achieved for individuals with the lowest levels of immunosuppression. For tuberculin-positive individuals, savings from a reduced number of active tuberculosis cases were greater than the costs of the intervention, even for low patient compliance levels. Preventive therapy for anergic persons can result in cost reductions at levels of tuberculosis infection of 15% or higher for a compliance level of at least 95%. For infection levels of less than 10%, cost-effectiveness ratios are unfavorable. Conclusions: Isoniazid preventive therapy administered to tuberculin- positive, HIV-infected patients increases life expectancies and reduces medical costs. Its extension to anergic patients may be justifiable on economic grounds in populations with a high prevalence of tuberculosis infection.