From Scientific American:
This revised timeline comes from a close examination of blood samples taken from men in the late 1970s for hepatitis B testing—including that of the man blamed for being the U.S. epidemic’s “Patient Zero.” For this new work researchers managed to isolate HIV in eight of those blood samples and sequence the viruses’ genomes. The genetic diversity of the HIV samples from those early dates lays bare the fact that the virus had been circulating—and mutating—in the country throughout the 1970s. The team’s molecular clock work even suggests that the U.S. strain of the virus had hopped from Africa to the Caribbean by about 1967, moved to New York City by about 1971 and from there to San Francisco by about 1976.
The virus’s family tree was sketched out by a group of international disease experts and a medical historian. They sequenced HIV genomes from patient blood samples and examined how the virus mutated over time. By comparing the eight genome sequences to earlier HIV samples from the Caribbean and Africa and assuming certain rates of mutation, the researchers found that there was already striking genomic diversity in the virus around the U.S. by the late 1970s. This suggests HIV had already been evolving within U.S. hosts for years. Similar genetic clock methods have also cleared 2014 World Cup soccer tournament fans of introducing the Zika virus to the Americas, and have helped epidemiologists track foodborne outbreaks.
The scientist who led the new HIV research, Michael Worobey, had published a paper in Proceedings of the National Academy of Sciences in 2007 suggesting a similar early introduction of HIV into the U.S.—but this drew serious skepticism. In this earlier work Worobey and his colleagues cited less-definitive evidence: They had studied viral gene samples from the 1980s, not whole genome …