Introduction

The first report of acquired immunodeficiency syndrome (AIDS) appeared in the June 5, 1981, edition of Morbidity and Mortality Weekly Report. It described five men who had sex with men (MSM) diagnosed with Pneumocystis carinii pneumonia (PCP). In 1984, researchers reported the discovery of a retrovirus, now known as Human Immunodeficiency Virus, type 1 (HIV-1), associated with AIDS. In 1986, researchers described a second strain, HIV-2, which shares 42% genetic homology with HIV-1 but is less virulent. Based on genetic sequence analysis, scientists have concluded that HIV-1 originated in the African chimpanzee and HIV-2 in the African sooty mangabey.

What is the epidemiology of HIV infection?

World

According to recent estimates, 40 million people worldwide are infected with HIV, and 3 million have died of AIDS in the past year.

Sub-Saharan Africa has been most severely affected, with the highest prevalence in Botswana, South Africa, and Zimbabwe. In Botswana, 36% of the adult population is infected with HIV. By the end of 1999, an estimated 10.7 million African children had lost one or both of their parents to AIDS.

Asia has also been affected by the epidemic. Thailand experienced a dramatic increase in heterosexually acquired HIV cases in the mid-1980s. About 80% of injection drug users (IDUs) in China are HIV seropositive, and the epidemic in the heterosexual population in India is growing rapidly.

In Eastern Europe, injection drug use is the main means of acquiring HIV. Ukraine has reported the majority of cases.