Thousands of more new HIV cases are occurring in the United States every year than was previously believed, according to new data from the U.S. Centers for Disease Control (CDC). Men who have sex with men (MSM) and African Americans remain disproportionately affected, according to the new estimates published in a special HIV/AIDS issue of the Journal of the American Medical Association, released August 3 to coincide with the start of the XVII International AIDS Conference in Mexico City, Mexico.

New technology and methodology developed by the CDC demonstrate that in 2006, an estimated 56,300 new HIV infections occurred in the US—substantially higher than the previous estimate of 40,000 new infections occurring annually.

The CDC notes that the new estimate does not represent an actual increase in the number of new HIV infections. An analysis conducted by the agency indicates that the annual number of new infections has remained fairly stable over the past decade, albeit a significantly higher number than was originally thought.

Many HIV-positive people are not diagnosed until years have passed since they were infected with the virus, hindering efforts to document the actual number of new infections within a certain time period. The new estimates were made possible using the Serological Testing Algorithm for Recent Seroconversions (STARHS), which allows researchers to distinguish recent from longstanding HIV infection.

The new estimates show that MSM of all races and ethnicities and African American men and women are the groups most affected by HIV. Fifty-three percent of all new infections in 2006 occurred in MSM. African Americans, while comprising 13 percent of the US population, accounted for 45 percent of the new HIV infections in 2006, with an annual infection rate that is seven times higher than that of whites and almost three times higher than that of Latinos.

On a more encouraging note, the CDC estimates indicate that HIV infections been relatively stable—or have been declining—among people who inject drugs, women of all races, and high-risk heterosexuals.