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.

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, said Dr. Kevin Reilly of the California Department of Health Services.

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Investigators continue to look at three other ranches in the areas in seeking the source of the contaminated fresh spinach.

"We are not saying this is the source at this point," Reilly said of the ranch.

Reilly told reporters the outbreak appears to be over. It sickened 204 people in 26 states and one Canadian province, he said.

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