The global situation
Although it has seemed a familiar enemy for the last 20 years, HIV/AIDS is only now beginning to be seen for what it is: a unique threat to human society, whose impact will be felt for generations to come. Today, an estimated 34–46 million people are living with HIV/AIDS. Already, more than 20 million people have died from AIDS, 3 million in 2003 alone (1). Four million children have been infected since the virus first appeared. Of the 5 million people who became infected with the virus in 2003, 700 000 were children, almost entirely as the result of transmission during pregnancy and childbirth, or from breastfeeding.
The most explosive growth of the epidemic occurred in the mid-1990s, especially in Africa (see Figure 1.1). In 2003, Africa was home to two-thirds of the world’s people living with HIV/AIDS, but only 11% of the world’s total population. Today, about one in 12 African adults is living with HIV/AIDS. One-fifth of the people infected with HIV live in Asia.
Globally, unprotected sexual intercourse between men and women is the predominant mode of transmission of the virus. In sub-Saharan Africa and the Caribbean, women are at least as likely as men to become infected.
Other important modes of transmission include unprotected penetrative sex between men, injecting drug use, and unsafe injections and blood transfusions. In many countries, including most countries in the Americas, Asia and Europe, HIV infection is mainly concentrated in populations engaging in high-risk behaviour, such as unprotected sex (particularly in the context of commercial sex work or between men) and sharing of drug injection equipment. In such situations, however, there is a persistent threat that localized epidemics will spill over into the wider population. In some countries, rapid growth of the size of the vulnerable populations – as a result of civil unrest, a rise in poverty or other social and economic factors – triggers epidemic growth and wider spread of the virus.
The prolonged time lag between infection with HIV and the onset of full disease (on average 9–11 years in the absence of treatment) means that the numbers of HIV- associated tuberculosis cases, AIDS cases and deaths have only recently reached epidemic levels in many of the severely affected countries. Globally, the greatest mortality impact is on people between the ages of 20 and 40 years. Dramatic changes in life expectancy can be observed in the most affected parts of the world. The pandemic has reversed decades of gradual gains in life expectancy in sub-Saharan Africa (2).
What does the global state of the pandemic mean in terms of progress towards the Millennium Development Goals? The eight goals, established following the historic Millennium Summit in New York in 2000, represent commitments by governments throughout the world to do more to reduce poverty and hunger and to tackle ill-health; specifically, to improve access to clean water and to reduce gender inequality, lack of education, and environmental degradation. This includes combating HIV/AIDS, and to have begun to reverse the spread of HIV by 2015. However, progress is not yet being made in many countries, and an unprecedented effort will be required in order for the worst-affected countries to make progress towards all of the Millennium Development Goals (see Box 1.1).
The uneven spread of HIV
A brief analysis of the regional spread of the HIV/AIDS pandemic shows major differences between regions, within regions and within countries, which have important implications for prevention, care and support. The striking differences in the size of the epidemics in sub-Saharan Africa and other regions of the world have been well documented. While almost all countries in sub-Saharan Africa have been severely affected, widening variations are also emerging within the region, indicating that the consequences of the pandemic will vary substantially (10).
The trends in HIV prevalence among pregnant women attending the same antenatal clinics since 1997 (see Figure 1.2) show that the epidemics in the countries of southern Africa are much larger than elsewhere in sub-Saharan Africa – and that the gaps appear to be widening. In eastern Africa HIV prevalence is now less than half that reported in southern Africa and there is evidence of a modest decline. In western Africa prevalence is now roughly one-fifth of that in southern Africa and no rapid growth is occurring. These striking differences are supported by data from population-based surveys and research studies (see Box 1.2). A range of socioeconomic, cultural, behavioural and biological factors are responsible, such as migration, male circumcision practices and the prevalence of herpes simplex virus type 2 infection (12, 13).
In most countries in Asia the epidemics tend to be concentrated in drug injecting and commercial sex networks, although Cambodia, Myanmar, Thailand and six states in India have an estimated HIV prevalence among adults of more than 1%. The course of the epidemics in the two most populous countries in the world – China and India – will have a decisive influence on the global pandemic. In 2003 it was estimated that 840 000 people in China were living with HIV/AIDS, corresponding to 0.12% of the total adult population aged 15–49 years. About 70% of these infections are thought to have resulted from injecting drug use or faulty plasma-collection procedures; over 80% of all those infected are men. Official estimates in India for 2003 put the number of people infected at 3.8–4.6 million, with considerable variation between states; there has been a modest increase in recent years.
Countries in eastern Europe and central Asia are experiencing growing epidemics, driven by injecting drug use and to a lesser extent by unsafe sex among young people. In the Russian Federation, where national prevalence is estimated to be just under 1%, 80% of people living with HIV/AIDS are under 30 years of age. In western Europe, the estimated number of new infections greatly exceeds the number of deaths, largely as a result of the success of antiretroviral therapy in lowering death rates. There are, however, worrying signs of increased incidence of other sexually transmitted infections, such as syphilis and gonorrhoea, and reported increases in risk behaviours in several countries (14, 15).
In the WHO Eastern Mediterranean Region it is estimated that there are around 750?000 people living with HIV/AIDS. Heterosexual sex is the main mode of transmission, accounting for nearly 55% of all reported cases. Injecting drug use has an increasing role in transmission and in the near future may become the driving force of the epidemics. A fivefold increase in infections among injecting drug users between 1999 and 2002 was recorded. In Sudan, the most affected country in the region, heterosexual sex is the predominant mode of spread.
In the Americas, the most affected area is the Caribbean, which has the second-highest prevalence in the world after sub-Saharan Africa: overall adult prevalence rates are 2–3%. In Latin America, an estimated 1.6 million people are now infected. Most countries here have concentrated epidemics, with injecting drug use and sex between men as the predominant modes of transmission. The predominant mode of transmission in the Caribbean is heterosexual sex, often associated with commercial sex work. In Central America, prevalence rates have been growing steadily and most countries there are facing a generalized epidemic. In the United States of America, 30 000–40 000 new infections occur every year, with African-Americans and Hispanics the most affected populations.
Rises in mortality, reductions in life expectancy
In many countries there is evidence of a reversal of the declines in child mortality achieved during the 1990s, especially in those most severely affected by HIV/AIDS. These reversals indicate the adverse impact of HIV/AIDS on the Millennium Development Goal of reducing child mortality. Once again, however, large variations between African countries in their HIV-prevalence trends and levels of child mortality not associated with HIV will mean very different impacts in different places. It has been estimated that HIV/AIDS was the primary cause of about 8% of deaths in under-fives in sub-Saharan Africa in 2001 (16).
In the absence of vital registration and reliable cause-of-death information, evidence on the impact of HIV infection on child mortality is limited. It is known, however, that even before the introduction of antiretroviral therapy the progression of disease among children infected with HIV in Europe and the USA was considerably slower than that observed in Africa. In western and eastern Africa the median survival time is less than two years, compared with well over five years in developed countries (17).
The most dramatic effect of the HIV/AIDS epidemic has been on adult mortality (18). In the worst-affected countries of eastern and southern Africa, the probability of a 15-year-old dying before reaching 60 years of age has risen sharply – from 10–30% in the mid-1980s to 30–60% at the start of the new millennium. In community-based studies in eastern Africa, mortality among adults infected with HIV was 10–20 times higher than in non-infected individuals (19). Overall, the greatest difference in mortality between infected and uninfected people is usually observed between the ages of 20 and 40 years. Women tend to die at an earlier age than men, reflecting the fact that the rates of HIV infection typically peak among women 5–10 years earlier than they do in men. The most reliable estimates of the median survival time following infection with HIV have come from the Masaka study in Uganda (20) where the figure was of the order of nine years – two years less than that observed in developed-country cohort studies even before the advent of effective treatment.
Vital registration systems, national censuses, demographic surveys and demographic surveillance systems have provided information on mortality trends (18). Census and survey data from Kenya, Malawi and Zimbabwe have revealed steadily rising adult mortality throughout the 1990s. In Kenya, the probability of dying between the ages of 15 and 60 years rose from 18% in the early 1990s to 48% by 2002 (see Annex Table 1). In Malawi the figure is now 63%; it was less than 30% in the early 1980s. In Zimbabwe, the 1997 probabilities of 50% for women and 65% for men have risen to an overall 80%. There is evidence that in Thailand and Trinidad and Tobago there have been increases in mortality, even though the prevalence of HIV infection is considerably lower in those countries than in most of Africa. In Thailand, for example, the crude mortality rate for those aged 15–49 years almost doubled from 2.8 to 5.4 per thousand between 1987 and 1996.
The advent of the HIV/AIDS pandemic has reversed the gains in life expectancy made in sub-Saharan Africa, which reached a peak of 49.2 years during the late 1980s and which is projected to drop to just under 46 years in the period 2000–2005 (2) (see Figure 1.3). This turnaround is most dramatic in those severely affected countries in southern Africa that had relatively high life expectancy prior to the appearance of HIV/AIDS. In Botswana, for example, life expectancy decreased from nearly 65 years in 1985–1990 to 40 years in 2000–2005; in South Africa it is expected to drop from over 60 years to below 50 years. The United Republic of Tanzania (whose epidemic is less than half the size of that in South Africa) is likely to have experienced a decline in life expectancy from 51 to 43 years in the last 15 years. In Nigeria (where the epidemic is about half the size of that in the United Republic of Tanzania) the gradual improvements that were being made have stalled.
Overall, life expectancy at birth in the African Region was 48 years in 2002; it would have been 54 years in the absence of HIV/AIDS. In the countries of southern Africa life expectancy would have been 56 years instead of 43 years (see Figure 1.4).