Scientists have discovered a strain of HIV in West Africa that progresses to AIDS in about five years, the shortest period of any type of prevalent HIV-1. The strain is called a recombinant virus, which comes about when an individual is infected with two different strains of HIV—there are over 60 epidemic strains worldwide—which eventually combine themselves into one. Swedish researchers studied 152 people with HIV in Guinea-Bissau, West Africa, where the strains known as 02AG and A3 are most common. A recombinant strain of those two, called A3/02, showed up in 13 percent of the study participants. Those with the recombinant strain had a nearly three-times greater risk of AIDS and AIDS-related death than the 29 percent of people who had A3. The estimated time of progression to AIDS or AIDS-related death was a respective 5 and 8 years for A3/02, 6 and 9 years for 02AG and 7 and 11 years for A3.