"Collectively, our data strongly suggest that the Haitian epidemic began with introduction of a V. cholerae strain into Haiti by human activity from a distant geographic source," the scientists write. The bacteria belong to a strain that evolved in South Asia. It was probably introduced onto Haiti by a sick person who flew there. We may never know who made the delivery, but it was a terrible blow not just to Haiti but perhaps to other New World countries. The South Asian strain is, unfortunately, deadlier than the Peru strain and resistant to antibiotics to boot. Waldor and his colleagues warn that unless the bacteria are stopped now, they could outcompete the milder Peru strain.
Incidentally (have I really not written about this before?) I highly, highly recommend The Ghost Map by Steven Johnson. It is the most fascinating book about cholera you will ever read.
I completely second this suggestion. It's not only the most fascinating book about cholera you will ever read, but also a great reminder about why living in cities is awesome, and why good infrastructure is a good idea. Oh, and why and how statistics save lives.