Lower AIDS Prediction Fuels Debate
The suggestion by two researchers that the AIDS epidemic has “crested” and will result in little more than 200,000 U.S. cases has reanimated the debate over the future course of one of the country’s most pressing public health problems.
The two former government epidemiologists have resurrected a 150-year-old epidemiological theory that states that epidemics follow the pattern of a bell-shaped curve. By that theory, called Farr’s law, they say the AIDS epidemic has been on the wane since late 1988.
But a host of other scientists say the theory may create false hope and ignores the peculiar complexity of the AIDS epidemic. With 1 million Americans believed infected with the AIDS virus, critics say the estimate of 200,000 cases will fall seriously short.
The debate, aired Friday in the Journal of the American Medical Assn., involves sometimes inscrutable epidemiologic arcana. But the outcome could be significant in the power of projections to influence funding for AIDS research, treatment and education.
“The risk, of course, is that those who don’t understand the nature of AIDS and HIV, or those who for a long time have been wishing it will just go away . . . may prematurely declare victory,” said Dr. James W. Curran of the U.S. Centers for Disease Control.
“And that’s, of course, not called for,” said Curran, the author of an editorial challenging the applicability of Farr’s law to AIDS. “But unfortunately, AIDS will get the best of these theories. We won’t have to wait long to find out they’re wrong.”
The Farr’s law theory is being aired by Dennis J. Bregman, a former CDC official who is now an assistant professor of preventive medicine at USC, and Dr. Alexander Langmuir, who retired in the 1970s as chief of epidemiology for the CDC.
Bregman and Langmuir base their projection on an 1840 law developed by pioneering epidemiologist William Farr. Farr fashioned the law after a smallpox epidemic in England and Wales, and refined it 25 years later after a severe outbreak of cattle plague.
Using reported cases of AIDS in the United States through 1987, and applying Farr’s principles, Bregman and Langmuir conclude by extrapolation that the AIDS epidemic peaked in late 1988 and the number of new cases being reported will bottom out in the mid-1990s.
“If our projection is right, we’re saying the epidemic might be only 25% of the size of what’s been projected,” Bregman said. “No one is even willing to consider the possibility that this epidemic is cresting and starting to decline.”
Indeed, Bregman and Langmuir’s approach is being challenged by other epidemiologists and biostatisticians with their own prognostications--based, for the most part, on more complex techniques that have been developed only in recent years.
In an editorial accompanying Bregman and Langmuir’s article, Curran and two other CDC officials contend that Farr’s law applies only to simpler epidemics--outbreaks in which the new infection is spread at a constant rate and among a well-defined group of people at risk.
The AIDS epidemic, by contrast, involves several different populations, different routes of transmission, geographical variations and a long and variable time in which the infection remains latent in the body before producing symptoms.
A separate research paper published in the same issue of the journal attempts to project the course of the AIDS epidemic in San Francisco. It takes into account such things as rates of infection and incubation, and the estimated number of people at risk.
The model projects that there will have been 12,349 to 17,022 AIDS cases in San Francisco by June, 1993. The study makes no national projection, but one of its authors said he and others have estimated 350,000 to 400,000 cases throughout the country by the end of 1993.
