Is CDC’s ‘Static’ AIDS Model ‘Politically Motivated?’ Columnist Asks

Reports from the CDC that the number of new HIV infections has "leveled off" are "more than a little misleading," columnist Linda Seebach writes in an opinion piece for the Scripps Howard News/Nando Times. Seebach states that according to CDC statistics, new HIV infections in the United States have held steady at 40,000 infections per year since 1992. "Isn't it more than a little odd that the number has scarcely changed in almost a decade when so much else about HIV and AIDS has changed in that time?" Seebach asks. She cites an article from the October issue of VitalSTATS, a newsletter from the not-for-profit Statistical Assessment Service, which addresses the issue of how HIV statistics are computed (Seebach, Scripps Howard News/Nando Times, 11/10).

Crunching Numbers
The VitalSTATS article states that the number of estimated new HIV infections has "stayed steady" every year since 1992, even though the number of positive HIV tests at publicly funded test sites has shown a "sharp decline" since 1991. Dr. John Karon of the CDC says that the agency's estimates for new infections are based on a mathematical model that does not rely on information garnered from test sites. He explained that to arrive at an estimate, the CDC first uses census data to calculate the number of sexually active males in the United States -- those between the ages of 18 and 44, or approximately 60 million men. The agency estimates the percentage of those men who are likely to be homosexual and "engaged in risky behavior" (1.2 million) and then subtracts the number of these men who are already believed to be HIV-positive (400,000). The CDC then estimates that 2% of HIV-negative gay men who engaged in risky behavior -- 16,000 men -- will become infected with HIV each year. However, the agency states that this figure represents only 60% of all new infections among men, and extrapolates this number to deduce that the number of total new HIV infections among men is approximately 27,000 per year. The CDC then estimates that approximately 30% of new HIV infections occur among women, and extrapolates the 27,000 figure to conclude that there are approximately 38,000 total new HIV infections each year in the United States. Most media outlets "conver[t]" 38,000 into 40,000, VitalSTATS reports. However, HIV surveillance data used in determining new infection estimates are based on reports from only 25 states, and there has been some dispute over whether 2% of gay men are actually engaged in risky behavior and how many of these men are likely to contract HIV each year. VitalSTATS reports that there are "reservations" over this method of calculation because it relies on a "static" model and the AIDS epidemic is constantly changing (VitalSTATS, October 2001).

Worldwide Estimates
Seebach notes that David Murray, director of the Statistical Assessment Service, questions "how accurate ... can worldwide estimates" of HIV cases be, especially if "it is essentially impossible to find out how rapidly people are becoming infected" in the United States. Murray, she writes, is "concerned" that in countries with "rudimentary medical infrastructure" deaths are being recorded as AIDS-related when no HIV diagnosis has ever been made. "That's a situation ripe for political exploitation," Seebach writes. She concludes, "There's no reason to believe the CDC's steady-state estimate of new infections is politically motivated, except the general one that politics influences just about everything having to do with AIDS. But that's reason enough to wonder" (Scripps Howard News/Nando Times, 11/10).