The nightmare that is the cholera epidemic of Haiti (2,100 dead so far) has become a little less mysterious. Haiti has not seen cholera for over a cenutry, and so the emergence of cholera in recent weeks has puzzled scientists and led to riots directed at the U.N. for supposedly bringing Vibrio cholerae to the Caribbean nation. Others have pointed to a New World strain as a potential culprit. It triggered an outbreak in Peru in 1991, and has circulated in Central and South America ever since. Perhaps these bacteria washed up on Haiti’s shores.

In the latest issue of the New England Journal of Medicine, Matthew Waldor of Harvard and his colleagues go some distance to settling the debate