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The study is the most detailed yet of the trends of HIV infection in young adults who are among the first generations to enter young-adulthood with the threat of HIV infection, said Rosenberg, and offers insight into how public health efforts have affected the course of the disease. Rosenberg and Biggar used AIDS cases reports to calculate the likely numbers of young people living with HIV and the rate of new infection with HIV in the years 1988 and 1993.
The researchers estimated that 50 percent fewer white men aged 18 to 27 were living with HIV infection in 1993 than in 1988. The authors attribute much of this decline to the striking drops in new infections of HIV acquired through homosexual contact in this group. The number of young minority men living with the HIV infection was roughly the same in 1988 and 1993, with rising rates of new infection through heterosexual contact offsetting declining rates of new infection through homosexual contact and injection drug use.
The number of black women aged 18 to 27 living with HIV infection in 1993 rose more than 60 percent from 1988. This jump is attributed to the increase in heterosexual transmission of the disease to women.
Rosenberg said he is cautiously optimistic that the trends showing declines in new cases of HIV attributed to homosexual contact and injection drug use have continued since 1993. "If fewer people have the disease, there is less chance of encountering an infected person," Rosenberg said, "which tends to slow the spread of the disease." Rosenberg also said it is possible that new therapies that reduce the viral load may also reduce the infectiousness of people carrying HIV.
The authors are particularly concerned by the high rate of heterosexual transmission among young minority individuals. According to the study, the percentage of minorities newly infected with HIV among the young is higher than the percentage of minorities in the general population.
"Most HIV-infected young people — about two-thirds — are black or Hispanic," Rosenberg said, but these minority groups constitute just 27 percent of the population of the age groups studied.
Rosenberg and Biggar used numbers of AIDS cases through 1995 for their calculations, working backwards to calculate the numbers of people living with HIV and the rate of new infection with HIV in the years 1988 and 1993. They focused on people ages 18 to 22 and ages 23 to 27 in each of those years. Each of these age groups was analyzed by gender, race/ethnicity (non-Hispanic white, non-Hispanic black, Hispanic, and other), and by mode of HIV transmission (homosexual contact, heterosexual contact, injection drug use, and men who had homosexual contact who also reported injection drug use). Data later than 1995 were not used due to the introduction of powerful new combination therapies in 1996, which slow the progression from HIV infection to full-blown AIDS. Because it calculates backward from current data, this method cannot identify HIV trends for the most recent several years. However, there is currently no direct survey of HIV rates in the general population as a whole that provides reliable data for adults in any age group, let alone for adults under 25 who are at relatively high risk.
* The study is titled, "Trends in HIV incidence among young adults in the United States." The authors are Philip S. Rosenberg, and Robert J. Biggar. Journal of the American Medical Association, Vol. 279, No. 23, June 17, 1998.
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