Social value of early antiretroviral treatment as HIV infection prevention

Background: Since 2007, HIV treatment guidelines have strongly recommended initiation of combination antiretroviral therapy (cART) when patient CD4 counts fall below 350 cells/mm3.[1] In response to evidence that cART initiation at higher CD4 levels was associated with reduced mortality and morbidity,[2] guidelines were updated in 2009 to recommend a threshold of 500 cells/mm3.[3] While cART has been shown to decrease the infectivity of HIV-positive individuals, the effect of early cART initiation (above 350 cells/mm3) on population incidence of HIV infection is uncertain. Purpose: To estimate the number and social value of HIV infections averted in the United States between 1996 (the year cART became available) and 2009 because of early cART initiation. Methods: A population disease transmission model was constructed for the period 1996 through 2009 and calibrated to US HIV incidence data.[4] Parameters associated with drug adherence, drug resistance, and HIV transmission were based on published estimates.[5-9] The model included four progressively severe states of HIV disease defined by CD4 levels, with the first three states roughly corresponding to CD4 counts in excess of 350 cells/µl. Untreated individuals moved through the four disease states and finally to death at a constant rate (4.9 years per state)[10], while treated individuals progressed through corresponding disease states to death at a slower rate (8.5 years per state). Untreated HIV-positive individuals initiated cART at a rate of 14% per year in the second disease state, increasing to 71% per year in the final state.[2] Societal cost estimates assumed a value for a life year of $200,000. Results: Cumulative HIV incidence in the US over the period 1996 through 2009 was predicted to be 748,000. Absent early cART treatment, cumulative incidence would have been 849,000 during this period. These 101,000 additional cases would have lost 11 years of life on average at a social cost of approximately $220 billion (undiscounted) and $90 billion (discounted at 3%). Conclusion: Based on this model, it appears that early cART initiation averted a substantial number of HIV infections in the US between 1996 and 2009, thereby preventing a considerable level of economic loss to society.