Early HIV treatment in the United States prevented nearly 13,500 infections per year during 1996-2009.

In recent years, guidelines for HIV treatment have recommended initiation of combination antiretroviral therapy (cART) earlier in the course of the disease than was previously the case. These recommendations stem in part from growing evidence that treatment reduces the risk of sexual transmission. We used an epidemiological model of disease transmission and progression to assess HIV prevention through early treatment-that is, initiation of cART when CD4 white blood cell counts are in excess of 350 cells per cubic millimeter. (CD4 cells are involved in the immune system's defense against tumors and infection; the number of CD4 cells in a cubic millimeter of blood is a standard measure of immune response to antiretroviral therapy.) We estimated that the actual timing of treatment initiation in the United States prevented 188,000 HIV cases in the period 1996-2009. "Very early" treatment (at CD4 counts greater than 500) accounted for four-fifths of the prevented cases. For all of the prevented cases, the losses in life expectancy that were avoided were worth $128 billion, assuming that a life-year has a value of $150,000. These findings underscore the cost-effectiveness of early HIV treatment.