Washington ? Wild pigs may have spread deadly bacteria onto a California spinach field, sparking an outbreak that killed three people and sickened more than 200 others nationwide, investigators said Thursday. They also said the outbreak appears to be over.

State and federal investigators have narrowed their focus to the ranch, where boar trampled fences that had hemmed in a spinach field.

Samples taken from a wild pig, as well as from stream water and cattle on the ranch, have tested positive for the same strain of E. coli implicated in the outbreak, Reilly said.