Medical News

HIV Transmission: Rate in U.S. Is Approximately 4 Percent Per Year

March 22, 2004

More than 95 percent of HIV-infected people in the United States do not transmit the virus to another individual in a year's time, according to a report by David Holtgrave, PhD, of Emory University's Rollins School of Public Health. In his analysis of the period 1978-2000, Holtgrave found that transmission rates dropped during the 1980s from essentially 100 percent to about 5.49 percent. The rate fell again slightly at the beginning of the 1990s, then remained relatively stable at 4.0-4.34 percent.

This rate is "rather surprisingly low," said Holtgrave. The drop "indicates a real success of HIV prevention programs and may help to explain why the number of new HIV infections has been rather stable at 40,000 infections per year for over a decade." But in what he called a "potentially important insight," Holtgrave noted that "the closer the transmission rate gets to 0 percent, the harder it will be to keep making continual reductions."

To calculate the annual HIV transmission rate, Holtgrave used the annual U.S. AIDS death statistics in 1978-2000 from CDC surveillance reports. Information on annual HIV incidence was obtained through a back calculation method; post-1990 HIV incidence data were drawn from CDC publications. To determine the number of people living with HIV/AIDS in any particular year, cumulative AIDS deaths for each year were subtracted from cumulative HIV incidence for that year. The annual HIV transmission rate was calculated by dividing adjusted HIV incidence for a given year by the estimated number of people living with HIV/AIDS in that year.

"At least 95 percent of persons living with HIV didn't transmit the disease to another person during any given year in the '90s," Holtgrave said. "Still, the transmission rates calculated in this paper also suggest we urgently need research to understand the societal, situations, behavioral and biologic reasons why the remaining infections still occur. What are the behavioral dynamics of partner relationships? How have HIV treatments reduced transmissibility? How do transmission rates vary by gender, age, race, ethnicity and other sociodemographic variables, and why? These are all critical questions that need to be answered so we can disrupt the remaining instances of transmission."

While the rates "likely will be approximately the same" in the next couple of years, "CDC has noted that the number of HIV diagnoses in the U.S. may be starting to rise again; if this trend continues, eventually we could see the transmission rate start to increase again," Holtgrave said. "But, we must keep in mind, the public health goal is not to keep the transmission rate the same or let it increase. We must find ways to decrease the transmission rate to even lower levels. Past HIV prevention work has been successful but we have much work to do."

The full report, "Estimation of Annual HIV Transmission Rates in the United States, 1978-2000," was published in the Journal of Acquired Immune Deficiency Syndromes (2004;35(1):89-92).

Back to other news for March 22, 2004

Adapted from:
AIDS Weekly

This article was provided by CDC National Prevention Information Network. It is a part of the publication CDC HIV/Hepatitis/STD/TB Prevention News Update.


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