Scientists have traced the genetic lineage of the new H1N1 swine flu to a strain that emerged in 1998 in U.S. factory farms, where it spread and mutated at an alarming rate. Experts warned then that a pocket of the virus would someday evolve to infect humans, perhaps setting off a global pandemic[although that, thankfully, doesn't appear to have happened].And, as 60 Second Earth notes (bold emphasis mine):
this H1N1 strain has not yet been found in the pigs near La Gloria [home to a factory farm with 950,000 pigs], nor is it clear how it would have jumped from the factory farm to little Edgar [Hernandez - "Patient Zero"].In other words, we haven't been able to implicate factory farming in Mexico for the disease mutating into a human strain, but can definitively link its original evolutionary kickstart to an American factory farm.
But what is clear thanks to the hard work of virologists is that this particular strain of flu got its genetic start on U.S. hog farms back in the 1990s. That's according to the U.S. Centers for Disease Control. How the virus jumped from pigs to humans may have nothing to do with factory farms, but confined animal feeding operations helped to breed the disease.