Health officials in New Mexico were able to genetically match a bacteria sample found in a bag of spinach to other findings, which narrowed the search for the source, the Washington Post reported.
David Acheson, a senior food safety official with the Food and Drug Administration told a news conference it was a major break.
"Yesterday, we narrowed it to California," he said. "Today, we narrowed it down to three counties. We're hoping to narrow it down to a field and ... to a spinach leaf."
Regardless, in a news release, the agency dealt another blow to the spinach industry, which has already lost an estimated $100 million, officials said.
"FDA advises consumers to not eat fresh spinach or products that contain fresh spinach until further notice," the release said.
The outbreak has killed one person and is suspected in another death, public health officials said.