Should the U.S. HIV epidemic follow current trends, it will eventually begin to shrink, aidsmap reports. Publishing their findings in AIDS & Behavior, researchers analyzed HIV prevalence, incidence and transmission rates between 2008 and 2012 according to data from the Centers for Disease Control and Prevention (CDC) and extrapolated those figures to 2015.

The National HIV/AIDS Strategy set a goal of reducing HIV incidence (the number of annual new transmissions of the virus) by 25 percent between 2010 and 2015, as well as reducing by 30 percent the forward transmission rate among people living with the virus.

Annual HIV diagnoses dropped from 40,698 in 2008 to 35,559 in 2012, while annual deaths dropped from 19,898 to 17,459 and the number of people living with HIV rose from 1.14 million to 1.22 million during that period. (Recent research suggests, however, that these HIV prevalence figures are overestimates.)

In 2008, people with HIV transmitted the virus to others at an annual rate of 0.035, equivalent to one transmission per person every 28 years. This figure dropped to 0.032 by 2010 and 0.029 by 2012, or one transmission per person every 34 years.

The researchers estimated that by the end of 2015, annual new diagnoses fell to 33,200, while deaths dropped to 16,100, meaning that 1.27 million people were living with the virus at that time. This translated to a further drop in transmission rates to 0.026, or one transmission per person every 38 years.

These figures mean the United States did not meet its National HIV/AIDS Strategy targets, with HIV incidence declining only 11 percent instead of 25 percent, and the transmission rate falling 17 percent rather than the hoped-for 30 percent.

The calculations further mean that, on average, each person with HIV would transmit the virus to 1.028 people based on 2008 figures (this statistical measure is called an R0 figure), to 0.913 people based on 2010 figures and to 0.754 people based on 2015 figures. Once this figure drops below 1.0, the epidemic is on course to contract. However, this effect will likely be delayed if people living with the virus die at a declining rate.

The researchers conducted a revised analysis accounting for people who die HIV positive but are never diagnosed. This estimate found that HIV incidence dropped 13 percent between 2010 and 2015, while the transmission rate fell 19 percent, to 0.0276, with an R0 of 0.797.

To read the aidsmap article, click here.