HIV/AIDS Incidence Revised Upward

The number of new HIV infections per year in the United States has been grossly underestimated for the past 20 years, according to an article published in today’s Journal of the American Medical Association (“Estimation of HIV Incidence in the United States.” JAMA 300:520-529, August 6, 2008.) The new estimate for HIV incidence is 56,300 new cases in 2006, 40% higher than previously reported by the CDC. The new data also show that the incidence of HIV has not declined at all since 1991, in sharp contrast to the previously estimated 50% decline since that time (compare Figure 1 in the JAMA article with Figure 9.24 in Human Biology, 5th ed., taken from official CDC data available at the time.) The total number of people living with HIV/AIDS is also expected to be revised upward, but those numbers will not be available until later this year.

How could the numbers have been so far off? For one, the new data are based on better testing methods that more precisely differentiate new HIV infections from long-standing ones. In addition, HIV infection rates are notoriously hard to come by, especially back in time. Even the new estimates are based on extrapolations using data from only 22 states. The CDC does the best it can do with limited data; the rest is an educated estimate.

Officials emphasize that this does not mean that there actually were more new cases of HIV – rather, we now have better estimates of the actual rates of new infection that existed at the time, regardless of whether or not they were accounted for. Nevertheless, some Democrats are criticizing the Bush administration for not doing enough to combat HIV/aids in this country. Senator Waxman of California released a statement last week in which he pointed out that the CDC budget for prevention has actually shrunk by 19% since 2002, and that the president recently requested a reduction in funding for HIV prevention at the CDC. Given that the incidence of HIV has not declined at all over the past 15 years, Senator Waxman may have a valid concern.

Students may react with a "So what are we supposed to believe, when even scientists can't get it right?" attitude. They'll need convincing that this kind of "flip-flop", as it would derisively be labeled in politics, is actually a normal part of a healthy scientific process.