Follow the poop. And it usually leads to water. Poop in the water, which then gets on produce.

Dr. David Acheson, the Food and Drug Administration’s food safety chief, has just told a congressional hearing in Washington that the Salmonella Saintpaul strain that has sickened 1,307 people in 43 States and Canada has been found in irrigation water and a serrano pepper at a Mexican farm.

Acheson said the farm is in Nuevo Leon, Mexico. Previously, the FDA had traced a contaminated jalapeno pepper to a farm in another part of Mexico.

Associated Press reports that if it turns out the tainted irrigation water was also used on tomatoes, it could provide some of the evidence that federal authorities are looking for to back their original focus on the fruit.