An Emory study estimates that more than 95 percent of Americans living with HIV do not transmit the virus to another person in a year's time. The findings were reported in the January issue of the Journal of Acquired Immune Deficiency Syndromes & Human Retrovirology .
David Holtgrave from the Rollins School of Public Health analyzed the period from 1978-2000. He found that HIV transmission rates dropped dramatically during the 1980s from essentially 100 percent to about 5.49 percent. With the onset of the 1990s, the rates fell slightly then remained relatively stable between 4.00-4.34 percent.
"The rate is rather surprisingly low," said Holtgrave, professor of behavioral science and health education. "The drop in the rate over the years indicates a real success of HIV prevention programs and may help to explain why the number of new infections has been rather stable, at 40,000 infections per year, for more than a decade. But the closer the transmission rate gets to zero, the harder it will be to keep making continual reductions. This is potentially an important insight.
"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 that we urgently need research to understand the societal, situational, behavioral and biologic reasons why the remaining infections still occur.
"What are the behavioral dynamics of partner relationships?" he continued. "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."
To calculate the annual HIV transmission rate (the number of new HIV infections in a year), Holtgrave obtained AIDS death statistics in the United States for the years 1978-2000 from the CDC's HIV/AIDS surveillance reports. Information about annual HIV incidence from 1978-90 was obtained from a back calculation method, and post-1990 data also was obtained from CDC HIV/AIDS publications. The cumulative number of AIDS deaths for each year was subtracted from the cumulative HIV incidence through that year to determine the number of people living with HIV/AIDS in any given year.
Finally, the annual HIV transmission rate was calculated by dividing the adjusted HIV incidence for a given year by the estimated number of people living with HIV in that year.
The HIV transmission rate, defined as the number of new HIV infections divided by the number of persons living with HIV/AIDS in a given year, was stable during the 1990s at just over 4 percent. This implies that some 95 percent of persons living with HIV in a given year do not transmit HIV.
"In the next couple of years, the rates likely will be approximately the same," Holtgrave said. "However, CDC has noted that the number of HIV diagnoses in the United States may be starting to increase; if this trend continues, eventually we could see the transmission rate start to increase again. 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."