Earlier this year, when more than 50 prominent American scientists were asked by a giant pharmaceutical concern to chart the future of the AIDS epidemic, they predicted that by the turn of the century more than 1 million Americans will have fallen ill from the disease.
Though the prediction was admittedly founded on instinct rather than solid epidemiological evidence, the headlines it generated and the comment it inspired illustrate the urgency being accorded the question of whether, and at what speed, the number of Americans infected with the AIDS virus will grow.
More than 35,000 Americans have gotten sick with AIDS, and more than 20,000 of them have died. But one California epidemiologist points out that
”what happens from now on depends on the rate at which people are being newly infected.”
Statisticians at the federal government`s Centers for Disease Control, near Atlanta, admit they have no good data on the rate at which the AIDS virus is spreading through the population. But they acknowledge that there are two potential avenues for growth.
The first is an increase in the number of infected individuals within each group known to be at risk of contracting AIDS, chiefly male homosexuals and intravenous drug users. The second, far more alarming but much less probable so far, is through an outbreak of AIDS into the general population.
Though there is no way short of massive testing to tell for sure whether increasing numbers of male homosexuals are becoming infected with AIDS, there is new and persuasive evidence that they are not.
One indication comes from a continuing study of 2,507 homo-sexual men in Los Angeles, Chicago, Baltimore and Pittsburgh, called the multicenter cohort study, in which the subjects are re-examined every six months. Thus far, the number of men newly infected with AIDS, or Acquired Immunodeficiency Syndrome, recorded in each six-month period has been half that of the preceding period. Another is found in a study of hundreds of blood samples drawn from San Francisco men by public health officials at regular intervals over the last nine years. The samples show that the number of men newly infected with AIDS is increasing by barely 2 percent a year, and that one-third of the men in the study have consistently remained AIDS-free.
A third, more indirect, indication is the decline in the incidence of other sexually transmitted infections among homosexual men. Most significant is the 73 percent drop in cases of rectal gonorrhea among men attending San Francisco city health department clinics between 1980 and 1984, because it suggests that anal sex, by far the riskiest form of sexual behavior with respect to AIDS, is waning.
Perhaps the most comprehensive study of how homosexual practices can contribute to the risk of AIDS is the San Francisco Men`s Health Study, a survey of more than 1,000 men randomly selected from households in and near the Castro district of San Francisco, the center of that city`s large homosexual community.
The study, which is continuing, has found that homosexual men who engaged only in oral-genital sex did not assume an ”excess risk of infection,” and that only those who practiced receptive anal sex had a ”significantly elevated” risk.
Another factor thought to have contributed to the spread of the AIDS virus among male homosexuals during the late 1970s and early 1980s is promiscuity, but several surveys have shown that homosexual men have sharply reduced the number of their sexual partners in recent years.
If the number of homosexual men infected with AIDS is not increasing, what about the number of intravenous drug users? Though most drug users known to have AIDS are men, more than half the women with AIDS-related illnesses have admitted using intravenous drugs. Four out of five drug users with AIDS are either black or Hispanic.
”The real concern is not sexual transmission,” says John Phair, a professor of medicine at Northwestern University involved with the multicenter cohort study. ”The real time bomb is intravenous drug abusers.”
Whether the time bomb will go off remains to be seen. Laboratory research has shown that the repeated use of an AIDS-infected needle is necessary before the likelihood of transmission increases measurably, and statistics compiled by the Centers for Disease Control show that, like the number of AIDS patients in general, the number of intravenous drug users getting sick because of AIDS is beginning to decline.
One explanation might be that most of those drug users who are at risk for AIDS already are infected with the virus. But it also may be that the campaigns against needle-sharing and for needle-cleansing directed at users in big cities on the East and West Coasts are making an impact.
For the last two years, for example, one San Francisco community group has been distributing small bottles of chlorine bleach to intravenous drug abusers in that city, along with comic-book instructions in English and Spanish on how to disinfect a hypodermic needle and syringe.
According to the group, three-quarters of more than 100 intravenous drug users it surveyed last summer, when the distribution program was a year old, were using the bleach to disinfect their needles.
For all the suffering it has wrought, the AIDS virus is not particularly hardy. It cannot survive for long in hot or dry places, and common household disinfectants such as Lysol or chlorine bleach have killed it readily in laboratory tests.
The second possibility for the growth of the infection pool–the spread of AIDS infection among those social groups not now recognized as entertaining any special risk–appears even less likely than the first.
Perhaps the strongest indication yet that the AIDS epidemic has not passed beyond the boundaries of the original risk groups comes from tests administered to federal employees by several government agencies, chiefly the Pentagon.
Since October, 1985, the Defense Department has tested nearly 2.5 million individuals, both prospective military recruits and active-duty personnel.
Only 3 in every 2,000 people tested under the Pentagon program have been found to carry the AIDS virus, a rate of infection that is exceedingly low for any communicable disease and far below the rate of AIDS infection for homosexuals and intravenous drug users.
Tests given to 10,572 Job Corps applicants during March and April produced a slightly higher rate, 3.8 infected per 2,000 applicants, while testing of 162,000 Army and Air National Guard members resulted in an even lower one, 1.4 infected per 2,000 guardsmen.
The Job Corps applicants tended to be somewhat younger and poorer than any other group tested, while the guardsmen were older and more affluent.
About 2,000 U.S. diplomats, their dependents and applicants for the Foreign Service also have been given the AIDS test, but a State Department spokeswoman said the results of those tests would not be made public, in part because the sample size was too small to be statistically significant.
Because of its enormous scope, and because the men and women it encompasses are mostly in their 20s and 30s, the age groups that are most sexually active and most at risk of AIDS, it is the Pentagon testing program that offers the brightest ray of hope.
Dr. Timothy Dondero, an epidemiologist who heads the Centers for Disease Control`s AIDS surveillance program, said in a recent interview that, despite the large numbers involved, the Pentagon program had been carefully administered from the beginning, with at least three blood enzyme assays for each person tested rather than the standard two.
He suspected, Dondero said, that there were fewer homosexuals and intravenous drug abusers among the military personnel and prospective recruits than among the general population, because individuals in both categories did not tend to volunteer as readily for military service.
But even if Dondero`s suspicions are correct, the test results would tend to be more indicative of infection rates for heterosexual men and women in general, once adjusted for age and sex.
Most important, however, is that the rate of infection among the military recruits, the second-largest group tested and slightly older than the Job Corps applicants, has not only remained approximately the same during 15 months of the testing program but even shown a ”small but significant decline” among young white men.
”I`m encouraged that we have not been able to document the predicted rise in the overall pattern of infection,” Dondero said.
Among the other tentative indications that AIDS has not begun to make substantial inroads among heterosexuals whose other behavior does not place them at risk of infection is that the AIDS virus has not begun showing up in great numbers among heterosexual patients seeking treatment at venereal disease clinics nationwide.
”For a heterosexual in Denver with no other risk factors, the rates are very low,” said Dr. David Cohn, the AIDS coordinator for the Denver Department of Public Health. ”In fact, they`re virtually nonexistent.”
Cohen said that one AIDS testing program there had surveyed nearly 7,500 men and women, three times as many so far this year as the year before. Last year, he said, those seeking AIDS tests had been about evenly divided between homosexuals and heterosexuals, while this year four out of five were heterosexual.
Potentially even more important than the question of how many Americans are infected with the AIDS virus today, or how many will be infected tomorrow, is the question of what proportion of those infected will ultimately sicken and die. As with the other conundrums surrounding the disease, the answer is murky at best.
In an article published in September, the Centers for Disease Control`s chief AIDS statistician, W. Meade Morgan, predicted that, barring development of an effective cure or a preventive vaccine, the number of Americans who have fallen ill because of AIDS might grow to 270,000 by the end of 1991.
That number, equal to the population of Tampa, or Fresno, Calif., has been widely reported; it is a centerpiece of the influential report on AIDS issued by U.S. Surgeon General C. Everett Koop. But invariably overlooked by those who cite the figure is the prediction`s 68 percent margin of error, which means that the total number of cases might be as low as 195,000.
Also overlooked is that the mathematical model on which the prediction is founded contains a number of untested assumptions, including the supposition that trends in the distribution of reported AIDS cases will not change.
Because the first cases of AIDS were not reported until June, 1981, the model also relies for its extrapolations entirely on data compiled since 1982, and Morgan acknowledged in a recent interview that ”predicting five years ahead on five years` worth of data is a little tricky.”
Whether the number of AIDS cases projected by the Centers for Disease Control will be recorded by the end of 1991 remains to be seen, but the federal agency`s model already has failed to fulfill some of its earliest projections. Though an additional 15,800 cases of AIDS were predicted for 1986, only 13,055 new cases were recorded last year.
Because the AIDS virus, which attacks and weakens the human immune system, can remain quiescent in the human body for longer than seven years without producing any overt physical symptoms of disease, many of the new AIDS cases recorded between now and 1991 may occur among individuals who already are infected.
Through a process not yet fully understood, the AIDS virus enters the bloodstream and attacks white blood cells that, as part of the body`s immune system, form a vital protective barrier against invading disease.
The cells, known as T-4 lymphocytes, have been aptly described as ”the conductors of the immune orchestra.” As the immune system is progressively weakened, the body becomes more vulnerable to other diseases, especially to a particular category of ”opportunistic” infections that ordinarily cannot get past a healthy immune system.
The two opportunistic diseases most common in AIDS patients are an unusual form of pneumonia and an equally rare kind of cancer. But the AIDS patient`s weakened immune system may also open the door to infections that result in other, more familiar symptoms–fatigue, diarrhea, unintentional weight loss and fever–that have been lumped together under the category of AIDS-related complex, or ARC.
A few people have fallen ill within weeks, even days after having been infected with the Human Immunodeficiency Virus, or HIV, as the AIDS virus is known. In some others, the virus has so far existed for longer than seven years without producing overt physical symptoms. The incubation times for most of those with AIDS fall somewhere in between.
How many cases of AIDS are ultimately recorded in this country will depend not only on the number of people infected with the virus, but the number in whom the infection will eventually lead to illness.
As recently as two years ago, researchers believed that only 10 percent or 15 percent of those infected with AIDS would sooner or later become ill. But as more time passes and more AIDS victims get sick, it is beginning to appear that the longer an individual carries the virus, the greater his chances of becoming ill.
”The more we study this disease the worse it looks for the people who are infected,” one researcher says. ”The longer we follow these men, the higher proportion of infected people get sick. The T-cell counts are going down, not for everyone but for the vast majority.”
Although the question of what it means to not get sick from AIDS borders on the metaphysical–such a judgment cannot be rendered for certain until a person infected with the AIDS virus has died from some natural and unrelated cause–few responsible researchers believe that all of those with the AIDS virus in their bloodstreams eventually will get sick.
Current estimates of the proportion that will not range from 30 percent to 70 percent, and there is new evidence that how rapidly the AIDS virus attacks the body`s immune system, and whether it wins or loses, may have as much to do with several other factors as with the presence of the virus itself.
If such ”cofactors,” as they are known, do exist, it could mean that some individuals who harbor them might be less susceptible to, or even immune from, AIDS. Though no cofactors for AIDS have been established conclusively, their existence is suggested by a number of so-far unexplained puzzles surrounding the disease.
Why, for example, do homosexual men with AIDS more often develop the rare cancer known as Kaposi`s sarcoma rather than pneumocystis carinii pneumonia, the most common opportunistic infection among other AIDS patients?
Why does it take only about three years for many of those who have become infected with AIDS through transfusions of contaminated blood to get sick, compared with five years or more for many homosexual men who became infected through anal intercourse?
Why do some groups of heterosexual Haitian men and women show rates of AIDS infection as high as 10 percent, while the incidence of AIDS among heterosexuals in the Dominican Republic, the Spanish-speaking nation with which Haiti shares the Caribbean island of Hispaniola, is virtually nil?
Why are incubation times for children with AIDS shorter than for adults?
Why are pipe smokers and men of British ancestry apparently at greater risk of acquiring AIDS than other men?
Various studies have long suggested that drug and alcohol use, anemia, malnutrition, general health and age all have an impact on the capacity of the body`s immune system to do its job of warding off infection. Thus, a young, healthy male with no history of substance abuse might be significantly less vulnerable to the AIDS virus than an older or less healthy individual.
The relationship between alcohol use and physical immunity may be an especially fertile field for further inquiry, because there is evidence that tuberculosis and certain kinds of cancers with characteristics similar to the AIDS virus occur several times more often in alcoholics than in the general population.
A second possibility is that the immune systems of individuals who have another retroviral infection, such as herpes simplex or hepatitis–both more common among homosexual men than the general population–are already partly weakened in the battle against that virus and thus less able to fend off the AIDS virus.
By far the most intriguing cofactor, however, might be genetic. A recent British study reported that an inherited protein appears to reduce the vulnerability to AIDS infection in the first place, and to slow the development of the disease among those who become infected anyway.
”Everybody`s very interested in this British report,” said a California epidemiologist. ”Within a matter of weeks you`re going to have a variety of laboratories around this country reporting on whether the finding is solid or not.”
