ARIZONA, U.S.A. (CMC):

A new study in the United States says HIV, the virus that causes AIDS, probably came into America from Haiti around 1969, a decade earlier than most scientists believed.

The study, 'The Emergence of HIV/AIDS in the Americas', was published Monday in The Proceedings of the National Academy of Sciences.

It is the work of Michael Worobey, an assistant professor of ecology and evolutionary biology at the University of Arizona in Tucson and his colleagues.

The stepping stone

"Our results show that the strain of virus that spawned the U.S. AIDS epidemic probably arrived in or around 1969. That is earlier than a lot of people had imagined," Worobey said.

"Haiti was the stepping stone the virus took when it left Central Africa and started its sweep around the world. Once the virus got to the U.S., it just moved explosively around the world."

The researchers found that most HIV/AIDS strains in the U.S. came from a single common ancestor that predates the well-storied 'Patient Zero' theory.

The Patient Zero theory came from a misrepresentation for Patient O, for 'Out of California', where early research on AIDS by the Atlanta-based U.S. Centers for Disease Control and Prevention (CDC) suggested HIV in the U.S. spread in the late 1970s and early 1980s from one man in California.