Earlier research . . . pointed to 1930 as the date when HIV jumped from West African chimpanzees into people, likely via hunters who butchered the apes. An unrecognized outbreak percolated in Africa for decades before jumping to Haiti . . . . There, the virus evolved into several variants. Most were dead-ends, causing few infections. But . . . a variant dubbed subtype B jumped from Haiti to the United States before igniting the current pandemic.
From Science News.
HIV-1 group M subtype B was the first HIV discovered and is the predominant variant of AIDS virus in most countries outside of sub-Saharan Africa. . . . subtype B likely moved from Africa to Haiti in or around 1966 (1962–1970) and then spread there for some years before successfully dispersing elsewhere. A "pandemic" clade, encompassing the vast majority of non-Haitian subtype B infections in the United States and elsewhere around the world, subsequently emerged after a single migration of the virus out of Haiti in or around 1969 (1966–1972). Haiti appears to have the oldest HIV/AIDS epidemic outside sub-Saharan Africa and the most genetically diverse subtype B epidemic . . . . HIV-1 circulated cryptically in the United States for 12 years before the recognition of AIDS in 1981.