About a third of them are younger than 30, nearly half are black, and more than half are men who have sex with men.
These startling figures arise from a new CDC analysis of HIV incidence, using a novel method that the agency believes is more accurate than earlier estimates.
In 2006, the CDC now says, about 56,500 people were newly infected in the U.S. The number is sharply higher than the estimate the CDC had been giving for recent years, of about 40,000 a year.
If the estimate is correct, more than 150 people are infected every day, or more than six an hour.
The new analysis "provides the first direct estimates of HIV incidence in the United States using laboratory technologies previously implemented only in clinic-based settings," said Irene Hall, Ph.D., of the CDC, and colleagues.
The study appears in the Aug. 6 issue of the Journal of the American Medical Association and was released here in conjunction with the 17th International AIDS Conference.
The new estimate is not directly comparable to earlier figures, Dr. Hall and colleagues said, and might be higher owing to bias in the new methods, limitations of the older methods, or higher HIV incidence.
But the new method is a "significant breakthrough," said Kevin Fenton, M.D., Ph.D., director of the CDC's National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention.
Speaking in a telephone press conference, Dr. Fenton said, "We have never before been able to directly measure new infections in the U.S. on a national level."
Previous estimates have been based on newly reported diagnoses, but were not able to establish when the infections took place. "We have not been able to see the leading edge of the epidemic," Dr. Fenton said.
The new figures were also derived initially from reports of new HIV diagnoses in 22 states, part of an expanded HIV surveillance network. The novel aspect of the analysis is the so-called BED HIV-1 capture enzyme immunoassay, which can distinguish recent from long-standing infections.
In 2006, the 22 states reported 39,400 new HIV diagnoses. Of those, 6,864 had specimens available to be tested using the BED assay and 2,133 ( 31%) were classified as recent infections. Extrapolating to the full U.S. yielded the 56,500 figure, whose 95% confidence interval ranged from 48,200 to 64,500. The estimated incidence rate was 22.8 per 100,000 people (with a 95% confidence interval from 19.5 to 26.1).
A statistical back-calculation yielded a similar number -- an estimated 55,400 new infections per year for 2003 through 2006, the researchers said. Dr. Fenton said new infections were probably never as low as the 40,000 figure and have been roughly stable since the late 1990s.
Analysis of the 2006 figures suggests that 34% of the newly infected were younger than 30, that 45% of them were black, and that 53% were men who have sex with men, Dr. Hall and colleagues reported.
"The bottom line is that the HIV epidemic in the U.S. continues to spread, and at a rate greater than was previously thought," according to Julie Davids, executive director of CHAMP, a New York-based advocacy group.
In a statement, Davids called for "the establishment of a comprehensive and accountable national AIDS strategy that will eliminate barriers to effective prevention, generate adequate resources, and hold our government accountable for ending this epidemic."
The implications of the new findings are unacceptable, said CDC director Julie Gerberding, M.D., and more must be done to lower infection rates. Dr. Gerberding, quoted by the New York Times, said "we are not effectively reaching men who have sex with men and African-Americans to lower their risk."
The CDC has been criticized for not releasing its figures earlier, preferring to wait until they could appear in a peer-reviewed journal.
- Reviewed by Dori F. Zaleznik, MD Associate Clinical Professor of Medicine, Harvard Medical School, Boston
Journal of the American Medical AssociationSource Reference: Hall HI, et al "Estimation of HIV Incidence in the United States" JAMA 2008; 300(5): 520-529.