What the history of AIDS may tell us about the future
More than 33.3 million people worldwide are living with HIV, and nearly 5,000 die every day. Each hour, around 200 people die of AIDS. There are around 7,400 new infections every day.11 The statistics are numbing, conveying the extraordinary human toll of the disease.
What was once a new disease has long since become familiar. The well-documented history of the epidemic tells us important facts that are relevant to the future. Consider some of the known facts.
Epidemics often differ radically within and between countries and regions
The so-called "global AIDS epidemic" is, in reality, an amalgamation of multiple local epidemics that often differ markedly from one another. Although women account for 60% or more of all people living with HIV in sub-Saharan Africa, men tend to predominate among HIV cases in most other regions.12 Whereas sexual intercourse is the primary mode of transmission in India overall, extremely high rates of infection are reported among people who inject drugs in certain districts.13 In Benin, Kenya, and Tanzania, the variation between the highest-prevalence district and the lowest is 12-fold, 15-fold, and 16-fold, respectively.14 Meanwhile, HIV prevalence in Côte d'Ivoire is more than twice as high as in Liberia or Guinea, even though these countries share national borders.15
These and other variations teach us is that AIDS programs and policies must address the unique set of circumstances in particular settings. Certain principles may apply to AIDS responses everywhere—such as the value of a rights-based approach or the importance of engaging affected communities in the response—but no cookie-cutter model exists for addressing the broadly divergent types of epidemics around the world.
The pandemic is constantly evolving
Even when epidemiological trends appear stable, the pandemic is constantly changing. As Figures 1.4–1.6 illustrate, what began as epidemics with differing characteristics primarily confined to a handful of countries progressively spread to affect the entire world.
Figure 1.4 Progress of the AIDS pandemic, 1990.
Source: Adapted from UNAIDS data.
Figure 1.5 Progress of the AIDS pandemic, 2000.
Source: Adapted from UNAIDS data.
Figure 1.6 Progress of the AIDS pandemic, 2009.
Source: Adapted from UNAIDS data.
Within regions and countries, the nature of individual epidemics has changed over time. In China, Eastern Europe, and Central Asia, epidemics that were previously characterized primarily by transmission via injecting drug use are now increasingly driven by sexual transmission.16 In many European countries, epidemics that were earlier concentrated in gay communities have given way to epidemics in which heterosexual adults and immigrants to the region are also at risk of infection.17 As the epidemic has matured and become endemic in sub-Saharan Africa, older adults in stable, long-term relationships now account for the largest share of new infections in many African countries.18
The evolution of each epidemic is affected by its social, economic, and physical environment
Patterns of social and economic life often determine the trajectory of local epidemics. In New York City, a "synergism of plagues," abetted by the planned shrinkage of municipal services as a result of the city's acute fiscal crisis in the 1970s, was directly tied to the explosion of HIV in the early 1980s among low-income drug users.19 The astonishing emergence of South Africa's HIV epidemic in the 1990s—with estimated HIV prevalence rising from less than 1% at the beginning of the decade to nearly 20% by the turn of the century—coincided with the dramatic social and population dislocations associated with the demise of apartheid. In Eastern Europe and Central Asia, the disintegration of the Soviet Union triggered radical shifts in sexual and drug-using behaviors and the rapid deterioration of public health services, contributing to sharp increases in HIV transmission.
The history of human relations and labor patterns in Southern Africa is indelibly tied to the epidemic's severity in that subregion. The countries with exceptionally high HIV prevalence are generally called "hyperendemic." Southern Africa is home to nine hyperendemic countries where adult HIV prevalence exceeds 10%, about which the aids2031 Hyperendemic Working Group concludes: "A central historical feature shared by all the hyperendemic countries was the rapid, forced proletarianization of males, the establishment of circular migratory patterns and, post-independence, large-scale urbanization."20 These trends triggered broad-scale migration of male workers, disrupted households, contributed to high rates of sexual concurrency, and destroyed traditional methods for setting social norms. The eventual results are evident in South Africa's rapidly growing informal urban settlements, where infection rates are twice the national average.21
The epidemic has become firmly entrenched in Southern Africa
AIDS is a pressing health challenge for scores of countries, but its effects are especially pronounced in Southern Africa. With just 2% of the world's population, Southern Africa accounts for 34% of all people living with HIV.22 It is impossible to speak of the future of Southern Africa without discussing the future of AIDS.
As Figure 1.7 reveals, the epidemic has skewed population structures in countries such as Lesotho. The figure for Ghana shows a more typical change in age structure resulting from lowered birth rates and improved life expectancy. By contrast, Lesotho, with one of the world's highest levels of HIV infection, shows a marked depletion of the population of working-age adults. In hyperendemic settings, the extraordinary loss of adults in their 30s and 40s has interrupted the natural process that imparts learning and values to younger generations, resulting in national populations that consist largely of the very young and the very old. These patterns not only reflect the epidemic's extraordinary impact, but also illustrate the degree to which AIDS undermines the ability of hyperendemic countries to mount a robust and sustained response to the epidemic.
Figure 1.7 Changes in population structure: Ghana and Lesotho.
Source: Population Division of the Department of Economic and Social Affairs of the United Nations Secretariat,World Population Prospects: The 2006 Revision.
Although AIDS epidemics began among the most affluent in some countries, they almost invariably visit their harshest effects on marginalized groups. Adult HIV prevalence for the world as a whole is 0.7%, yet an estimated 13% of people who inject drugs, 6% of men who have sex with men, and 3% of sex workers are living with HIV.29 Moreover, these global estimates, derived from national surveys, significantly understate the pandemic's burden on these populations in particular settings. National surveys in Malawi, for example, indicate that more than 70% of sex workers in the country are infected.30 Even in sub-Saharan Africa, where heterosexual intercourse has long been assumed to be the almost exclusive driver of epidemics, recent studies have documented exceptionally high HIV prevalence among these key populations. As Figure 1.10 illustrates, multiple studies have documented levels of HIV infection among men who have sex with men that consistently exceed overall adult HIV prevalence in these settings. In Kenya, men who have sex with men, people who inject drugs, and sex workers and their clients account for roughly one in three new HIV infections.31 In Senegal, men who have sex with men are believed to represent up to 20% of all incident infections.32
Figure 1.10 HIV prevalence among men who have sex with men in sub-Saharan Africa (2002–2008). [Note: South Africa 1 and 2 and Kenya 1 and 2 refer to the results from different studies.]
Source: WHO/UNAIDS 2009 AIDS epidemic update.
The pandemic's history cautions us to anticipate unexpected turns over the next generation
Although HIV information systems remain weak in many countries (an issue that Chapter 2, "Generating knowledge for the future," addresses in some detail), the ability to monitor and understand national epidemics has greatly improved. After experiencing a rapid increase during its first 15 years, the pandemic appears to have stabilized globally, with the annual number of new infections about 20% lower today than in the mid-1990s.33 With the exception of Eastern Europe and Central Asia, where new infections continue to increase, the pandemic appears to have stabilized or slowed in most regions.
This apparent stabilization of the pandemic has given rise to a general consensus in the popular media that the future of the pandemic can be projected with some accuracy. AIDS, it is said, has "peaked," with a slow but steady decline in rates of new infections likely to occur in the foreseeable future.
This emerging confidence in our ability to predict the future of the pandemic ignores previous experience with other infectious diseases and with AIDS itself.34 Studies of endemic syphilis, for example, have documented that waves of infections are common over time, with spikes in incident cases often separated by a decade or more.35 This is especially likely for epidemics that have become concentrated in particular populations. After a sharp decline in HIV incidence among men who have sex with men more than two decades ago in high-income countries, rates of new infections have steadily increased since the early 1990s.36 In part, this reflects the fact that new cohorts of young people enter the population of sexually active adults over time.
Indeed, AIDS has repeatedly defied predictions and is sure to do so in the future. In December 1995, the WHO Global Programme on AIDS erroneously projected that the pandemic's center would be in Southeast Asia, with more modest growth predicted in sub-Saharan Africa.37 A decade ago, few would have predicted that more than 1 million people would be living with HIV today in the Russian Federation. And certainly few observers foresaw a reversal in Uganda's longstanding gains in reducing HIV prevalence.38 On the more favorable side of the ledger, only a small number of scientists were prepared for the emergence in the mid-1990s of combination antiretroviral therapy, which, for those who had access to it, rapidly converted the disease from an invariably fatal condition to one that is chronic and manageable.
The pandemic's past teaches that political, economic, and social shocks can greatly affect the trajectory of AIDS. In this regard, the accelerating rate of population migration in many regions is cause for concern. A study of six Asian countries by the aids2031 Working Group on Countries in Rapid Economic Transition concludes that major, continued population movements, particularly associated with growing urbanization, may facilitate the spread of HIV over the next generation.39 In China alone, 300 million people are expected to migrate over the next 20 to 30 years.40 Although mobility on its own is not a risk factor for HIV, migration often increases risk and vulnerability by disrupting social and familial networks, contributing to sexual risk taking and drug use, and subjecting individuals to violence and discrimination. In Asia, population migration has been strongly linked with the spread of infectious diseases.41
Other changes are also foreseeable. The introduction of antiretroviral therapy in resource-limited settings is rapidly altering attitudes about AIDS in many parts of the world where infection has long been regarded as a death sentence. Although the availability of treatment is arguably a prerequisite for a strong, sustainable effort to prevent new HIV infections (an issue Chapter 4, "Financing AIDS programs over the next generation," addresses in greater detail), the health benefits of treatment may also cause some to view the disease with less concern and alarm. In high-income countries, especially among men who have sex with men, evidence indicates that sharp reductions in HIV-related death and illness have contributed to an increase in sexual risk behaviors, ultimately resulting in rises in HIV incidence.42 Were such trends to be replicated elsewhere, the results could be potentially catastrophic.
In short, much about the future of the pandemic remains unclear. This uncertainty necessitates continued vigilance in the AIDS effort worldwide.