Oct 13, 2006 (CIDRAP News) Investigators seeking the contamination source in a nationwide Escherichia coli O157:H7 outbreak have genetically matched an E coli strain found in manure from a California cattle ranch near spinach fields with the strain isolated from sick patients and their leftover spinach.
In a statement yesterday, the US 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. Thus, the FDA has narrowed its investigation from nine farms to four, which are located in Monterey and San Benito counties.
Media reports say 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.
Findings raise more questions
Kevin Reilly, deputy director of prevention services for the California Department of Health Services, told reporters at a press conference yesterday that the results don't prove that the manure was responsible for the outbreak.
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 still don't know how the feces contaminated the spinach. Suspected transport mechanisms include agricultural runoff, irrigation water, and farm-worker hygiene.
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.
The positive finding is significant but is just one aspect of the investigation, the FDA said. Testing of other environmental samples from all four ranches is ongoing.
"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.
The outbreak has sickened 199 people and killed 3, and has spanned 26 states and one Canadian province. Since 1995, 20 E coli outbreaks have been traced to leafy greens. Just last week, Nunes Company, Inc., a Salinas, Calif. produce marketer, recalled its green leaf lettuce because of possible E coli contamination from a secondary irrigation water source. In an Oct 10 press release the company said its follow-up tests on the recalled lettuce and irrigation water were negative for E coli O157:H7.
Risky farming practices?
The pasture where the contaminated cattle manure was found is part of a ranch that leases fields to spinach growers, according to an article today in the San Francisco Chronicle. Fences on the property had been penetrated by wild pigs, and investigators are assessing whether the pigs might have spread the bacteria from the cattle pasture to the spinach field, the Chronicle said.
Reilly told the Chronicle the farm where matching manure was found did not fully follow voluntary guidelines that growers use to prevent contamination of leafy greens. He said concerns include the proximity of the cattle to spinach fields and the failure of fences to keep wildlife out of the growing fields.
"The fields are surrounded, frankly, by pastures where livestock are kept," Reilly told reporters. Reilly was quoted by the Times as saying the closeness of cattle to leafy greens farms is not uncommon in the Salinas Valley area, but that not all four of the suspected farms have both livestock and produce operations.
The Times reported that the cattle ranch and nearby spinach operations are separated by a paved road and fences. The ranch has not been identified.
Foodborne disease expert Craig Hedberg, PhD, told CIDRAP News that the spinach outbreak highlights a lack of attention to sanitation on farms and how that translates into disease risk. "This is going to make it impossible for the industry not to deal with these issues in the future," said Hedberg, an associate professor of environmental and occupational health at the University of Minnesota in Minneapolis,
The spinach outbreak is the produce industry's "Jack in the Box" moment, Hedberg said, referring to a nationwide, hamburger-linked E coli O157:H7 outbreak that killed four and sickened hundreds in 1993. "The Jack in the Box episode changed perceptions of eating hamburger and led to changes in how we slaughter cattle and prepare meat," he said. "The spinach outbreak will usher in a series of changes in how we manage farms and the environment and handle fresh produce."
Hedberg said he's not surprised that the investigators were able to locate a possible source. "With the scope of the outbreak and the attention it got, much more effort was put into the investigation," he said, noting that federal and state authorities had a lot of data to work with, such as product case numbers and spinach samples.
Oct 12 FDA statement