Twenty years after the first clinical evidence of acquired immunodeficiency syndrome was reported, AIDS has become the most devastating disease humankind has ever faced. Since the epidemic began, more than 60 million people have been infected with the virus. HIV/AIDS is now the leading cause of death in sub-Saharan Africa. Worldwide, it is the fourth-biggest killer.

At the end of 2001, an estimated 40 million people globally were living with HIV. In many parts of the developing world, the majority of new infections occur in young adults, with young women especially vulnerable. About one-third of those currently living with HIV/AIDS are aged 15-24. Most of them do not know they carry the virus. Many millions more know nothing or too little about HIV to protect themselves against it.

• Eastern Europe and Central Asia: Still the Fastest-Growing Epidemic
  Eastern Europe -- especially the Russian Federation -- continues to experience the fastest-growing epidemic in the world, with the number of new HIV infections rising steeply. In 2001, there were an estimated 250,000 new infections in this region, bringing to 1 million the number of people living with HIV. Given the high levels of other sexually transmitted infections, and the high rates of injecting drug use among young people, the epidemic looks set to grow considerably.

• Asia and the Pacific: Narrowing Windows of Opportunity
  In Asia and the Pacific, an estimated 7.1 million people are now living with HIV/AIDS. The epidemic claimed the lives of 435,000 people in the region in 2001. The apparently low national prevalence rates in many countries in this region are dangerously deceptive. They hide localized epidemics in different areas, including some of the world's most populous countries. There is a serious threat of major, generalized epidemics. But, as Cambodia and Thailand have shown, prompt, large-scale prevention programmes can hold the epidemic at bay. In Cambodia, concerted efforts, driven by strong political leadership and public commitment, lowered HIV prevalence among pregnant women to 2.3% at the end of 2000 -- down by almost a third from 1997.

• Sub-Saharan Africa: The Crisis Grows
  AIDS killed 2.3 million African people in 2001. The estimated 3.4 million new HIV infections in sub-Saharan Africa in the past year mean that 28.1 million Africans now live with the virus. Without adequate treatment and care, most of them will not survive the next decade. Recent antenatal clinic data show that several parts of southern Africa have now joined Botswana with prevalence rates among pregnant women exceeding 30%. In West Africa, at least five countries are experiencing serious epidemics, with adult HIV prevalence exceeding 5%. However, HIV prevalence among adults continues to fall in Uganda, while there is evidence that prevalence among young people (especially women) is dropping in some parts of the continent.

• The Middle East and North Africa: Slow but Marked Spread
  In the Middle East and North Africa, the number of people living with HIV now totals 440,000. The epidemic's advance is most marked in countries (such as Djibouti, Somalia and the Sudan) that are already experiencing complex emergencies. While HIV prevalence continues to be low in most countries in the region, increasing numbers of HIV infections are being detected in several countries, including the Islamic Republic of Iran, the Libyan Arab Jamahiriya and Pakistan.

• High-Income Countries: Resurgent Epidemic Threatens
  A larger epidemic also threatens to develop in the high-income countries, where over 75,000 people acquired HIV in 2001, bringing to 1.5 million the total number of people living with HIV/AIDS. Recent advances in treatment and care in these countries are not being consistently matched with enough progress on the prevention front. New evidence of rising HIV infection rates in North America, parts of Europe and Australia is emerging. Unsafe sex, reflected in outbreaks of sexually transmitted infections, and widespread injecting drug use are propelling these epidemics, which, at the same time, are shifting more towards deprived communities.

• Latin America and the Caribbean: Diverse Epidemics
  An estimated 1.8 million adults and children are living with HIV in Latin America and the Caribbean -- a region that is experiencing diverse epidemics. With an average adult HIV prevalence of approximately 2%, the Caribbean is the second-most affected region in the world. But relatively low national HIV prevalence rates in most South and Central American countries mask the fact that the epidemic is already firmly lodged among specific population groups. These countries can avert more extensive epidemics by stepping up their responses now.