Agents from the FBI and the Office of Criminal Investigations in the Food and Drug Administration executed search warrants Tuesday at two growers and distributors in the Salinas Valley, the New York Times reported.
The U.S. Attorney for the Northern District of California, Kevin Ryan, said there is no evidence the contamination was deliberate, but negligence was a possibility.
"We are investigating allegations that certain spinach growers and distributors may not have taken all necessary or appropriate steps to ensure that their spinach was safe before it was placed into interstate commerce," Ryan said.
Of the 193 people who became ill from the O157:H7 E. coli bacteria strain in 26 states and Canada, 98 had to be hospitalized, the FDA said.
Five Salinas-area companies have voluntarily recalled their spinach products since the outbreak was reported nearly three weeks ago, the Times said.