The cost-effectiveness of expanded testing for primary HIV infection.

PURPOSE Primary infection with the human immunodeficiency virus (HIV) is a major factor in the HIV epidemic. Most patients become symptomatic and seek care, but seldom are they tested or is their condition diagnosed. The objectives of this study are to determine whether it is cost-effective to expand testing for primary HIV infection to a larger cohort of patients, and, if so, which diagnostic assay is most cost-effective. METHODS We undertook a cost-effectiveness analysis of testing a hypothetical cohort of more than 3 million outpatients with fever and other viral symptoms regardless of HIV risk factors using 3 diagnostic assays: p24 antigen enzyme immunosorbent assay (EIA), HIV-1 RNA assay, and third-generation HIV-1 EIA. Antiretroviral therapy was started when the CD4 cell count decreased to 350/microL. Outcome measures were the incremental cost-effectiveness of the diagnostic assays, number of cases identified, cases avoided in sexual partners, and threshold prevalence. For sensitivity analyses, we used 50,000 dollars as the threshold for cost-effectiveness. RESULTS At the baseline prevalence of 0.66%, p24 antigen EIA testing was the most cost-effective option at a cost of 30,800 dollars per quality-adjusted life-year gained when compared with no testing. There were 17,054 cases identified, and infection was avoided in 435 partners. Probabilistic sensitivity analysis, in which the estimates for all variables are varied simultaneously, determined that expanded testing with p24 antigen EIA compared with no testing had a 67% probability of being cost-effective at the baseline prevalence and a 71% probability at a prevalence of 1%. CONCLUSIONS Expanded testing for primary HIV infection with p24 antigen EIA may be a sound expenditure of health care resources.