By Liz Highleyman

HIV incidence, or the number of new infections, in the U.S. has not previously been measured directly. While standard HIV antibody tests show whether or not a person has the virus, they cannot determine how recently infection occurred, and many people are diagnosed with HIV long after they become infected. In addition, several states have reported only AIDS cases, not HIV infections, by name in previous years, leading to incomplete data.

In a media briefing on August 2, in advance of the XVII International AIDS Conference in Mexico City, officials with the Centers for Disease Control and Prevention (CDC) released new estimates for yearly HIV infections; the figures were also published in the August 6, 2008 Journal of the American Medical Association.

CDC investigators used the new Serologic Testing Algorithm for Recent HIV Seroconversions (STARHS) method, employing a modified antibody test called the BED HIV-1 capture enzyme immunoassay that can determine whether infection occurred within the past 5 months.

They analyzed a subset of 6864 leftover serum samples from the 39,400 individuals aged 13 or older who were newly diagnosed as HIV positive during 2006 in 22 states with consistent name-based HIV reporting.

The investigators also used back-calculation methods to produce revised historical estimates for HIV infections occurring during 1977-2006, based on HIV diagnoses from 40 states and AIDS cases from all 50 states and the District of Columbia.

Results

31% of the tested samples (2133 out of 6864) were classified as recent HIV infections.

Based on extrapolations from these data, there were an estimated 56,300 new infections in the U.S. in 2006.

The estimated HIV incidence rate for the U.S. population as a whole was 22.8 per 100,000 persons.

Just over half of all new infections (28,700, or 53%) occurred in men who have sex with men (MSM), a group that has experienced an increase in incidence.

16,800 new infections, or 31%, occurred in people presumably exposed through heterosexual contact.

Injection drug users accounted for 6,600 new infections (12%), representing a decreased incidence from prior years.

27% of all new infections occurred in women.

Blacks accounted for 45% of new infections, compared with 35% for whites and 17% for Latinos.

Incidence rates by race/ethnicity were 83.7 per 100,000 persons among blacks, 29.3 per 100,000 persons among Latinos, and 11.5 per 100,000 persons among whites.

The back-calculation yielded an estimate of 55,400 new infections during the 2003-2006 period.

"This study provides the first direct estimates of HIV incidence in the United States using laboratory technologies previously implemented only in clinic-based settings," the authors wrote in conclusion. "New HIV infections in the United States remain concentrated among men who have sex with men and among black individuals."

In discussing their back-calculation findings, the study authors noted that for the entire U.S. population, the annual number of new infections probably peaked at around 130,000 in the mid-1980s, fell to a low of about 49,000 in the early 1990s, increased again to about 58,000 in the late 1990s, then declined slightly after 1999 and remained stable at around 55,000.

However, they concluded that the number of new infections has probably never been as low as 40,000, the figure CDC has been quoting for annual incidence for several years. In fact, the current best estimate of 56,300 for 2006 is 40% larger than the long-standing CDC estimate.

Community advocates have known for several months that CDC was preparing to release updated numbers, and the agency came under considerable criticism for its delay. Even UNAIDS Executive Director Peter Piot said at the conference's opening press conference that he didn't understand why the CDC had taken so long. However, CDC Director Julie Gerberding said the agency wanted the data to go through a thorough independent peer review by a respected medical journal before releasing it to the public.

Kevin Fenton

Speaking to the media, Kevin Fenton, Director of the CDC's National Center for HIV/AIDS, Viral Hepatitis, STD and TB Prevention, said "It's important to note that the new estimate does not represent an actual increase in the number of new infections, but reflects our ability to more precisely measure HIV incidence and secure a better understanding of the epidemic. This new picture reveals that the HIV epidemic is, and has been, worse than previously known and underscores the challenges in confronting this disease."

"Too many Americans continue to be affected by this disease," he added. "These new findings emphasize the importance of reaching all HIV-infected individuals and those at risk with effective prevention programs."

Advocates took the opportunity of the announcement of the new higher numbers to criticize what they said was inadequate funding of domestic HIV prevention and testing programs, even as Congress allocates more money for HIV/AIDS relief in poor countries.

The jump in the estimates caught the attention of the presidential candidates, who so far have mainly avoided speaking about HIV/AIDS. Republican nominee John McCain stated, "By focusing efforts on reducing drug costs through greater market competition, promoting prevention efforts, encouraging testing, targeting communities with high infection rates, strengthening research and reducing disparities through effective public outreach, we as a nation can make great progress in fighting HIV/AIDS."

"These new figures should bring new focus to our efforts to address AIDS and HIV here at home," said presumptive Democratic nominee Barack Obama. "Combating HIV/AIDS also demands closing the gaps in opportunity that exist in our society so that we can strengthen our public health. We must also overcome the stigma that surrounds HIV/AIDS -- a stigma that is too often tied to homophobia. We need to encourage folks to get tested and accelerate HIV/AIDS research toward an effective cure because we have a moral obligation to join together to meet this challenge, and to do so with the urgency this epidemic demands."

8/5/08

Sources

HI Hall, R Song, P Rhodes, and others. Estimation of HIV Incidence in the United States. Journal of the American Medical Association 300(5): 520-529. August 6, 2008.

Centers for Disease Control and Prevention. New technology reveals higher number of new HIV infections in the United States than previously known. Media release. August 3, 2008.

R Wolitski (National Center for HIV/AIDS, Viral Hepatitis, STD and TB Prevention). Dear Colleague letter. Augus 2, 2008