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Although the number of people living with HIV has increased in the United States over time, the rate at which an infected person passes the virus on to an uninfected person has dropped significantly since the peak of the epidemic, according to a study by researchers at the Johns ��ѻ��ý and the Centers for Disease Control and Prevention (CDC). Researchers found the rate of transmission dropped 88 percent since 1984 and 33 percent since 1997. The study will be published in a letter to  and is available in advance of publication on the journal’s website.

“For every 100 persons living with HIV today 5 or fewer will transmit the virus to an uninfected person in a given year,” said , PhD, lead author of the study and chair of the Bloomberg School’s . “In other words, 95 percent or more of those living with HIV do not transmit the virus to others, which indicates that prevention efforts are having a real impact.”

Holtgrave and his colleagues based their analysis on the CDC’s latest HIV incidence data. According to the study, the annual transmission rate in 1984 was 44 per 100 persons with HIV. The annual rate dropped to 6.6 per 100 persons by the early 1990s. The transmission rate rose slightly in 1997 to 7.5 per 100 persons when new antiretroviral therapies were first introduced, which researchers said may have led some persons at risk for HIV to disregard prevention measures. By 2006, the transmission rate dropped to just under 5 per 100.

“The declines reflect the success of prevention efforts across the nation,” said Richard Wolitski, PhD, study co-author and acting director of CDC's Division of HIV/AIDS Prevention. “However, despite this success, we cannot forget that new HIV infections are increasing among gay and bisexual men and that African Americans and Hispanics continue to experience disproportionate and unacceptably high rates of HIV and AIDS. The fight against HIV is far from over.”

Additional authors of “Updated Annual HIV Transmission Rates in the United States, 1997-2006” are H. Irene Hall, PhD, and Philip H. Rhodes, PhD, of the CDC.

The research was not funded by a specific grant.