The U.S. Centers for Disease Control and Prevention (CDC) missed more than 16,000 new HIV infections in its last tally of the disease, according to a new analysis.

The CDC reported in the Journal of the American Medical Association yesterday that its 2006 estimate of new HIV infections in the U.S. was 40 percent off: 56,000 contracted the human immunodeficiency virus—the virus that leads to full-blown AIDS—that year, not 40,000.

Here's why they got it wrong: First, previous estimates relied on extrapolating from limited data taken from small studies on HIV incidence in high-risk populations, like men who have sex with men. Also, the earlier estimates did not take advantage of a new HIV test (called STARHS or Serological Testing Algorithm for Recent HIV Seroconversion), which can tell whether a person has been infected within the last six months. Beforehand, researchers only knew that someone had been diagnosed with HIV, not when someone contracted the virus—and many people diagnosed with HIV contracted it several months or even years prior.

The CDC now says that the number of new HIV cases in a year has never fallen as low as 40,000, but plateaued at around 55,000 since 1999. The agency spends $750 million per year to prevent new infections, but the data suggests that the gains of the 1990s are being pushed back.

CDC prevention expert Kevin Fenton told The Washington Post that the agency's campaigns were not reaching "all those that need it," especially gay black men. Men who have sex with men account for 53 percent of new infections; African-Americans made up 45 percent of new cases.

Rich Wolitski, the CDC's acting director of the Division of HIV/AIDS Prevention, said in a CDC podcast that while the epidemic has stabilized, it has done so "at an unacceptably high level."

(Photo: iStockphoto/Amanda Rohde)