NEW YORK (Reuters Health) – Using new immunoassay technology, researchers estimate that the number of new HIV infections among adolescents and adults in 2006 was 56,300, substantially higher than earlier estimates, according to a report by the HIV Incidence Surveillance Group.

The BED HIV-1 capture enzyme immunoassay (BED) distinguishes seroconversion within the previous 6 months from long-standing infections, the Group explains in the Journal of the American Medical Association for August 6.

Led by Dr. H. Irene Hall at the Centers for Disease Control and Prevention in Atlanta, the research group retested remnant diagnostic serum specimens from patients age 13 years and older who were newly diagnosed in 2006. Included were 6864 specimens from 22 states, of which 31% were classified as recent infections according to BED.

By extrapolating from these data, the incidence rate in 2006 was 56,300, equivalent to 22.8 per 100,000 population. Earlier estimates based on cohort studies had placed the incidence closer to 40,000 infections per year.

Demographic data indicate that roughly three out of four new infections in 2006 occurred among males, and that more than half occurred among men who have sex with men (MSM). Compared with whites, the HIV incidence was seven times higher among blacks and three times higher among Hispanics.

According to model estimates, peak HIV incidence occurred in 1984-1985 at 130,000 incident infections per year, followed by a nadir in the early 1990s at 49,000 per year. Incidence again peaked at 58,000 in the late 1990s, then remained stable at 55,000 per year.

Among injection drug users, HIV incidence has decreased by approximately 80% since the late 1990s, the authors report. In contrast, the incidence among MSM was lowest in the early 1990s and increased thereafter.

“This suggests that without incidence data, delays may occur in recognizing a resurgence of HIV infections among certain populations,” Dr. Hall’s group maintains, “which in turn may delay implementation of needed prevention efforts.”

“A substantial reduction in HIV incidence will require wider implementation of the effective interventions currently available and the development of additional interventions, such as antiretroviral chemoprophylaxis or a vaccine,” they conclude.

JAMA 2008;300:520-529.