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SALINAS, Calif. -- Investigators seeking the source of contamination in a nationwide E. coli O157:H7 outbreak have genetically matched the strain with manure from a California cattle ranch located near spinach fields.
In a statement issued late last week, the U.S. Food and Drug Administration (FDA) said the investigation points to one infected lot of contaminated spinach that contained spinach from fields on four different farms. Samples of cattle feces on one of the implicated ranches tested positive based on matching genetic fingerprints for the same strain of E. coli that sickened 199 people.
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The trace-back investigation was narrowed from four farms to nine; the suspect farms are located in Monterey and San Benito counties. Testing continues of other environmental samples from all four ranches that supplied the implicated lot of contaminated spinach.
The FDA's positive test result is a significant finding, but is just one aspect of the investigation. "While the focus of this outbreak has narrowed to these four fields, the history of E coli O157:H7 outbreaks linked to leafy greens indicates an ongoing problem," the FDA said.
Media reports said three manure samples tested positive for the outbreak strain, and that investigators have so far taken 650 samples from soil, water, and manure on the farms. The manure samples that tested positive for the outbreak strain were located between a half-mile and a mile from a spinach field, the Los Angeles Times reported.
However, federal and state investigators said they still don't know for certain how the feces contaminated the spinach, although agricultural runoff, irrigation water, and farm-worker hygiene are among the chief suspects.
Media reports said this is the first time investigators have been able to link an outbreak strain of E coli to a farm where contaminated spinach or lettuce was grown.
Aside from FDA, other agencies involved in the ongoing investigation that is seeking to determine the cause and scope of the E. coli O157:H7 outbreak linked to fresh spinach include: the State of California, the Centers for Disease Control and Prevention (CDC) and the United States Department of Agriculture (USDA)