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3
The Future Course of the Epidemic
and Available National Resources
Short- and long-term estimates of the magnitude, pattern, and trends of
AIDS and other HIV-related conditions are crucial to health care planning
efforts and to the design of prevention and treatment strategies. One of
the major problems in planning these efforts has been that, because AIDS
is a relatively new disease and HIV is an unusual virus, there is little
previous experience on which to base predictions about the epidemic's
behavior. This chapter describes what can be projected on the basis of
present knowledge and the resources that can be brought to bear on
current and anticipated problems. (Chapter 5 discusses the implications of
current projections for the provision and financing of health care and
psychosocial support for those with HIV-related conditions. Chapter 6
identifies epidemiologic and other areas of research that must be pursued
so that better predictions can be made.)
PROJECTIONS BY THE PUBLIC HEALTH SERVICE
Following a June 1986 planning conference at Coolfont, Berkeley
Springs, West Virginia, the Public Health Service (PHS) issued updated
projections of the incidence and prevalence of AIDS by 1991 (see
Appendix G). Following is a summary of the major projections made by
the PHS:
· There are 1 million to 1.5 million Americans currently infected with
HIV. Of these, 20 to 30 percent are expected to develop AIDS by 1991.
85
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86 CONFRONTING AIDS
· By the end of 1991 there will have been a cumulative total of more
than 270,000 cases of AIDS in the United States, with more than 74,000
of those occurring in 1991 alone.
· By the end of 1991 there will have been a cumulative total of more
than 179,000 deaths from AIDS in the United States, with 54,000 of those
occurring in 1991 alone.
· Because the typical time between infection with HIV and the de-
velopment of clinical AIDS is four or more years, most of the persons
who will develop AIDS between now and 1991 already are infected.
· The vast majority of AIDS cases will continue to come from the
currently recognized high-risk groups.
· New AIDS cases in men and women acquired through heterosexual
contact will increase from 1,100 in 1986 to almost 7,000 in 1991. This
figure includes those heterosexuals reporting contact with people known
to be infected or with people in known high-risk groups and heterosexuals
who are presumed to have acquired the disease from contact with
individuals not known to be in such groups.
· Pediatric AIDS cases will increase almost 10-fold in the next five
years, to more than 3,000 cumulative cases by the end of 1991.
PROBLEMS IN MAKING PROJECTIONS
There are substantial uncertainties about such factors as the prevalence
of HIV infection, the rate of transmission of the virus among various
population groups, and the risks of disease among those infected.
Accordingly, any projection of the future incidence and prevalence of
AIDS (whether by the PHS or by others) will be subject to considerable
uncertainty.
Nevertheless, empirical projections of the incidence, prevalence, and
cost of AIDS, however crude or uncertain, are essential for planning a
response to the epidemic. The critical issue is to identify the value and
limitations of such projections and their policy implications so that
improved projections of the burden of disease can be developed. Also, by
assessing the limits of such models, the data that need to be collected can
be identified.
The PHS estimates of the incidence of AIDS were derived from an
empirical model based on a statistical trend analysis of AIDS cases
reported to the CDC through May 1986 (Morgan and Curran, 1986~. A
very similar statistical model was used in earlier projections based on
reported cases through mid-1985 (Curran et al., 1985; W. M. Morgan,
Centers for Disease Control, personal communication, 19861. Such mod-
els depend on the assumption that observed trends in a disease, such as
the distribution of cases by age, sex, geographic location, and risk group,
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THE FUTURE COURSE OF THE EPIDEMIC 87
will not change with time. They are adequate for reasonable short-term
projections but are of far more limited use for long-term projections (e.g.,
rr.ore than five years).
Obviously, more complex models that incorporate known information
on the sizes of populations at risk, viral transmission and infectivity, and
the natural history of HIV infection and its associated diseases would be
expected to yield more accurate, and thus more valuable, predictions.
However, the data in those areas necessary to construct such models
were considered by the committee's Epidemiology Working Group to be
limited in the following ways:
1. There are no survey data that can be considered to accurately
represent the general population. Surveys to date include those of blood
donors seen at blood banks after voluntary deferral of donation by
high-risk individuals was requested; applicants for military service, who
are a disproportionately young, minority, and economically disadvan-
taged population; and members of high-risk groups. These groups are
almost certainly not representative of the general population, and how to
analyze data obtained from them to deduce what is happening in the
general population is not known.
2. In high-risk groups (for example, homosexual men) there is wide
variation among communities in the prevalence of disease and sero-
positivity, based on location, age, and possibly frequency of high-risk
behaviors (such as anal intercourse). This makes difficult the estimation of
national prevalence in high-risk groups, or even estimates of the likely
spread within these groups.
3. There are major differences as to the time when the virus was
introduced into communities in various parts of the country, even among
the same high-risk groups. Given the long and uncertain time lag between
lIIV infection and symptoms of that infection, this variation makes
extrapolation from the number of AIDS cases meeting the CDC definition
to the likely number of infected persons at a given time nationwide very
tenuous.
4. The natural history of the disease is not yet fully defined. The
proportion of infected persons who will develop AIDS or ARC is not yet
known, nor is the time frame for the occurrence of these conditions.
Thus, estimates useful in health care planning, such as hospital days
required for treatment or days of work lost, are very difficult to derive.
Empirical models do not have to take into account these poorly
understood factors to enable projections of the epidemic's future. How-
ever, they suffer from their own set of uncertainties. Though case reports
to the CDC constitute the most reliable source of analysis of AIDS trends,
such data have important limitations. First, the CDC criteria (Appendix
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88 CONFRONTING AIDS
E) are undoubtedly too restrictive to include all serious manifestations of
HIV infection. If the mix of manifestations of HIV infection changes over
time, the predictions from empirical models will be inaccurate.
Second, cases of AIDS that meet the CDC criteria may be underre-
ported, although the extent of underreporting is not known reliably. As
long as underreporting rates have not varied over time, empirical analysis
of time trends in reported AIDS cases would remain unbiased. However,
increasing awareness of the main modes of acquiring AIDS and its
decreasing novelty make it plausible that underreporting has increased as
the disease has become more common, a phenomenon that has occurred
with other diseases. If so, purely empirical models of AIDS trends will
show a spurious deceleration of the epidemic.
Third, there are delays in reporting cases to the CDC. Accordingly, the
time series of cumulatively reported cases understates the actual number
diagnosed, especially for more recent months. In an empirical analysis of
trends in the incidence of AIDS, the observed data on diagnosed cases
need to be corrected for reporting lags. Because such corrections will
mostly affect recent data, apparently minor changes in the correction
method can significantly affect distant projections from time trend mod-
els. The method that CDC uses to correct for such delays assumes that
the distribution of delays between the diagnosis and the report of the case
to the CDC remains constant over time (Curran et al., 19851. Such an
assumption needs careful and regular scrutiny.
Fourth, statistical confidence intervals (see Appendix G) surrounding
future projections from empirical models are mathematically and biolog-
ically problematic because there is little basis for estimating the distribu-
tion of errors.
Fifth, projections of the prevalence of AIDS are based not only on
projections of the incidence of AIDS but on estimates of the life
expectancy of future AIDS victims. If changes in the natural history of the
epidemic or improvements in medical care result in prolongation of life for
AIDS patients, the prevalence of the disease would rise even faster than
the incidence. The prevalence of disease is an indicator of the number of
AIDS patients that will be alive and in need of health care.
Cases of AIDS that are diagnosed in the near future will reflect the
consequences of past infection. Therefore, despite the uncertainties
discussed above, the PHS projections (and those of other purely empirical
models) are likely to be highly accurate in the short term. Consequently,
despite the fact that current projection methods are crude, it is reasonable
to assume that the rising incidence of AIDS will not soon reverse itself.
Disease and death resulting from HIV infection are likely to be increasing
5 to 10 years from now and probably into the next century.
The committee believes that the PHS estimates are reasonable at this
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THE FUTURE COURSE OF THE EPIDEMIC 89
time and supports their use for planning purposes. However, its accep-
tance of these projections does not imply that they are precise, nor does
it obviate the need to continue to acquire data that will permit the
construction of more sophisticated models.
THE EPIDEMIC WITHIN AND BEYOND HIGH-RISK GROUPS
The populations at highest risk for HIV infection in the near future will
continue to be homosexual men and IV drug users, but no accurate data
exist on the size of these groups. It is also not known with what frequency
homosexual men practice the behaviors (primarily receptive anal inter-
course) that put them at high risk of HIV infection. Thus, the distribution
of risk within the total group of men at risk because of homosexual
activity is not known, nor can the likely rate of spread be calculated.
Estimates of the overall percentage of the male homosexual population
infected with HIV must take into account the definition of the population
under consideration. Lower estimates of the prevalence of seropositivity
are usually associated with larger estimates of the total homosexual
population (encompassing individuals who presumably have had fewer
homosexual encounters). Given this consideration, the committee's Epi-
demiology Working Group estimated that seropositivity among male
homosexuals ranges from over 50 percent in some areas for men who
have had a large number of partners to under 20 percent for a population
including any individual who has participated in homosexual activity.
By far the largest number of persons now seropositive in the United
States presumably acquired their infection through homosexual activity.
However, as discussed in Chapter 4, there is evidence that the spread of
HIV through homosexual activity has slowed. The trend is attributed to
behavioral change in response to the AIDS epidemic, but it may also be
that many persons in the highest-risk subgroup (those with the most
partners) have already been infected. HIV infection will probably con-
tinue to spread in homosexual males, although possibly at a slower rate
because of the use by some of "safer sex" practices (e.g., avoidance of
intercourse with infected persons, increased use of condoms, and avoid-
ance of anal intercourse).
The numbers infected and at risk among IV drug users are even more
difficult to estimate. The total number of IV drug users in the United
States is not known, and persons move in and out of the group rather
frequently. Although evidence indicates that there has been some modi-
fication of behavior in response to the AIDS epidemic, behavioral
modification is much less pervasive in this high-risk group than among
male homosexuals (see Chapter 4~. In locales such as New York City
where needles and syringes are extensively shared, many IV drug users
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90 CONFRONTING AIDS
may have already been exposed, but this may not be true for other urban
centers. Continuing spread of HIV in IV drug users throughout the United
States is expected in the future.
There is a broad spectrum of opinion about the extent of the likely
spread in the United States of HIV infection in the heterosexual popula-
tion, but there is strong agreement that the present surveillance systems
have only limited capacity to detect such spread. Because of the much
larger size of this population as compared with the recognized high-risk
groups, there is potential for wide-ranging estimates. Opinions provided
to the committee by members of the Epidemiology Working Group
ranged from the estimate of HIV infection as a minor problem among
heterosexuals to an estimate that perhaps millions of heterosexuals who
have multiple sex partners or who patronize prostitutes will ultimately be
affected.
In central Africa, bidirectional heterosexual transmission is believed to
be the dominant mode of transmission (Mann, 19861. Interpretations of
the data from Africa are complicated, however, by large numbers of
sexual partners and by frequent prostitute contact among heterosexual
African AIDS patients and by reports of repeated use of unsterile needles
and syringes in many medical care settings.
Whatever the efficiency of heterosexual transmission, it is clear that the
infection will continue to be amplified among populations in countries or
regions with a high prevalence of infection by frequent transfusion of
blood (unless screening of the blood supply begins), by the vertical
transmission of infection to mother and child, and by the continued
medical use of unsterile needles. Thus, the disease will continue to
increase dramatically in those areas.
In the United States, where such amplification will generally not be
present, it is presumed that heterosexual spread will be slower. However,
IV drug use in some communities or groups may amplify sexual trans-
mission. Much of the male-to-female spread of HIV infection in the
United States has been associated with IV drug use and has been
confounded by the possibility that the women are also IV drug users. The
relatively high seropositivity in some prostitute groups has also been
attributed to IV drug use. A small amount of data is beginning to appear
on the proportion of male homosexuals who also have heterosexual
contact. The figure may be as high as 10 to 20 percent, and these
individuals represent a large reservoir for potential infection of women
and their offspring and for further heterosexual spread of infection. In this
regard, it should be noted that the PHS projections of the future number
of heterosexually acquired cases are based on the observations of the
heterosexual spread that has occurred thus far in the epidemic predom-
inantly heterosexual transmission from individuals who became infected
through IV drug use or homosexual activity (as in the case of bisexuals).
.
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THE FUTURE COURSE OF THE EPIDEMIC 91
It is not known how the infection will behave when spread in that segment
of the heterosexual population which has no other risk factors
(Winkelstein et al., 19861.
Overall, the committee concludes that over the next 5 to 10 years there
will be substantially more HIV infections in the heterosexual population
and that these cases will occur predominantly in those subgroups of the
population at risk for other sexually transmitted diseases. These cases are
expected initially to occur mainly in the geographic areas and among the
demographic groups that already have a high frequency of AIDS or IV
drug abuse. In addition, increased HIV infection in infants is expected as
more women in their childbearing years become infected, but this may be
moderated by screening, as discussed in Chapter 4. (See Chapter 6 for
recommendations of studies that would track the course of the epidemic
through heterosexual contact and permit interventions to be appropriately
targeted.)
THE PROPORTION OF SEROPOSITIVE INDIVIDUALS
WHO WILL DEVELOP AIDS
Opinions in the Epidemiology Working Group varied widely regarding
the proportion of seropositive persons who will eventually die of HIV-
related causes. At this time, there are only five years of observations on
which to base such predictions. The data now available show that the
proportion of a cohort of seropositive individuals that have progressed to
AIDS is still rising five years after infection. Furthermore, once infected,
a person may well remain at risk of clinical disease for life. With some of
the less common clinical manifestations, particularly those that are
necrologic, there may be a very long delay after infection.
The estimate provided to the committee by the Epidemiology Working
Group was that 25 to 50 percent of seropositive persons will develop
AIDS as defined by the CDC within 5 to 10 years of seroconversion, and
that a higher percentage cannot be ruled out on the basis of present
studies. This estimate is consistent with but goes beyond that of the PHS,
which projected that 20 to 30 percent of currently seropositive individuals
will be diagnosed with AIDS within 5 years (Appendix G). In addition,
there is an increasing number of reports of manifestations of HIV
infection that fall outside the CDC definition of AIDS, which therefore
modify projections upward.
LONG-TERM PROSPECTS
HIV infection is likely to continue to spread among those individuals
who engage in behavior known to transmit the virus. HIV infection
behaves somewhat like hepatitis B. but a number of factors make it
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92 CONFRONTING AIDS
difficult to predict whether it will reach or exceed the prevalence of that
disease. These factors include the asymptomatic period after HIV infec-
tion, which facilitates "silent" spread of the virus, the presumed lifelong
infectivity of all infected individuals, the lack of data on the efficiency of
transmission, and the difficulty of predicting changes in behavior and
transmission that education may generate. There is also insufficient
knowledge at this time to predict how the virus will evolve in its
apparently new (human) host. Therefore, it is impossible, whether by
model or by analogy, to predict the long-term course of the epidemic with
any degree of certainty.
It is clear, however, that reducing transmission is a difficult proposi-
tion. Because no vaccine is likely to become available in the near future
(see Chapter 6) and because of the seriousness of the disease, the only
prudent course of action is an immediate, major effort to stop the further
spread of infection through public health measures, particularly educa-
tion. Any delay will bequeath to future policymakers a problem of
potentially catastrophic proportions and will condemn many thousands of
individuals to infection and disease.
NATIONAL RESOURCES FOR DEALING WITH AIDS AND HIV
There are many organizations, groups, and individuals that could be
drawn upon to address aspects of the public health measures (Chapter 4),
health care (Chapter 5), or research (Chapter 6) related to AIDS and HIV
infection. Additionally, the epidemic has prompted the development of
new groups to address certain problems and the extension of existing
groups into new areas. This is particularly true of male homosexuals, who
have developed community support groups. Former drug users have also
conducted educational efforts. There are many resources spread across
both the public and private sectors; thus, many of the needed actions can
and perhaps should be undertaken by groups at both levels.
A complete inventory of the national resources available for dealing
with AIDS and HIV infection would include information on existing and
potential activities or areas of concern (e.g., research, health care,
education), on the nature of each resource (e.g., pharmaceutical com-
pany, community group), and on the level of activities (e.g., national,
state, local, risk group). Appendix D lists various groups and organiza-
tions that are already active or that could be enlisted to work against
AIDS and HIV infection.
Impediments to Involvement
Many of the groups and organizations listed in Appendix D have al-
ready been engaged in problems related to AIDS and HIV infection that
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THE FUTURE COURSE OF THE EPIDEMIC 93
are appropriate to their capabilities, often with considerable success. But,
in the judgment of the committee, owner important resour`;~s In uoc~ `~c
public and private sector have not yet become appropriately engaged or
have addressed relevant problems inadequately.
The reasons for noninvolvement vary, but they include the following:
]; ~, . . .. ..
· lack of awareness about the magnitude of the problem and the needs
· slowness in responding to obvious needs
· apparent reluctance or inability to pursue particular programs be-
cause of political, ideological, moral, or religious considerations, includ-
ing the social stigma associated with some of the risk groups
· lack of appropriate recruitment efforts
· lack of funds or other resources (e.g., facilities) for pursuing prom-
ising opportunities
· lack of appropriate inducements to enter the field (e.g., stability of
funding)
· perceptions regarding the availability of reagents or other resources
necessary for productive research
· specific commercial disincentives (e.g., liability for vaccine-related
injuries, uncertainty over market size and public health policy)
· insufficient development of the basic research data base upon which
further commercial development might proceed
· uncertainty with regard to federal agency responsibilities
Some of these impediments may be removed by relatively simple
actions recommended in other parts of this report. Others are more
complex and may require new mechanisms or more time to be reduced.
Mechanisms for Coordinating Activities
Mechanisms exist for coordinating certain facets of the overall ap-
proach to AIDS and other HIV-related problems. Within the executive
branch, the Public Health Service has developed a plan to guide its
constituent agencies (Appendix G). The committee concurs in general
terms with the overall goals and approaches outlined in this plan.
However, the plan focuses on only part of the federal government's
activities and potential. Though the Public Health Service is a significant
resource, it represents only a portion of the national capacity to address
the problems caused by HIV infection. Other groups, such as the military
and the Department of Education, are also well situated to conduct
certain types of epidemiologic or clinical research.
No individual in the Public Health Service currently has primary
responsibility for identifying priorities in implementing the PHS plan, but
a Public Health Service AIDS Task Force has been established and a
coordinator appointed. Certain activities will require contributions from
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94 CONFRONTING AIDS
various federal agencies outside the PHS, such as the Department of
Defense and the Department of Education. Furthermore, many activities
outlined in the plan might be better conducted with broad participation of
nonfederal groups. No formal mechanisms exist for ensuring efficient
collaboration in these areas.
Certain task forces under the AIDS coordinator of the Public Health
Service have responsibility for monitoring efforts conducted by the PHS
agencies with their purview. The committee believes that while these task
forces may promote communication within and between federal agencies,
they sometimes have not sufficiently engaged or informed other relevant
national resources and have not identified priorities and devised or
articulated the strategic plans necessary to attain the desired goals in the
shortest possible time.
In many areas, there are no mechanisms for ensuring concerted action
against AIDS and HIV infection, especially where activities involve
diverse public and private sector bodies. Five important areas where this
is the case are (1) vaccine and drug development, (2) epidemiologic and
natural history studies in the United States and abroad, (3) evaluation of
models for the appropriate care of HIV-associated conditions, (4) the
financing of that care, and (5) the U.S. contribution to international
efforts. Each of these subjects is considered in detail in the chapters that
follow.
There is a need to mobilize all existing resources through more effective
interaction between the public and private sectors. To meet this need, and
also to inform the American public, Congress, and the executive branch,
the committee proposes the establishment of a National Commission on
AIDS. Such a body should be advisory to existing administrative entities.
(For fuller discussion of this recommendation, see Chapter 1.)
REFERENCES
Curran, J. W., W. M. Morgan, A. M. Hardy, H. W. Jaffe, W. W. Darrow, and W. R.
Dowdle. 1985. The epidemiology of AIDS: Current status and future prospects. Science
229: 1352-1357.
Mann, J. M. 1986. The epidemiology of LAV/HTLV-III In Africa. P. 101 in Abstracts of the
Second International Conference on AIDS, Paris, June 23-25, 1986.
Morgan, W. M., and J. W. Curran. 1986. Acquired immunodeficiency syndrome: Current
and future trends. Pub. Health Rep. 101:459-465.
Winkelstein, W., J. A. Wiley, N. Padian, and J. Levy. 1986. Potential for transmission of
AIDS-associated retrovirus from bisexual men in San Francisco to their female sexual
contacts. JAMA 255:901.
Representative terms from entire chapter:
drug users
