E. coli bacteria a persistent threat to leafy greens crops

In a display of detective skills worthy of Sherlock Holmes, state and federal investigators hunted down the bacteria that caused 205 people in 26 states to become ill and three to die last September after they ate bagged California spinach.

The final report issued March 21 could not pinpoint the smoking gun that fired the fatal bullets. What investigators found was an arsenal of guns, and plenty of potentially lethal bullets ready to be fired. While one farm, the Paicenes Ranch, was identified as the source of this particular batch of E. coli O157:H7, the bacteria was also found on three other farms growing spinach for Natural Selections Foods.

E. coli O157:H7, a virulent strain of a common bacteria, may be more widespread than once believed and not necessarily associated with feedlot cattle and confined animal feeding practices – at least in California’s Salinas Valley. Once thought to occur mostly in cattle on high-grain diets, this E. coli strain was found in the manure of pastured cattle and wild pigs and in soil and water they came in contact with.

“The Salinas Valley appears to have seasonal, systemic E. coli O157:H7 contamination in the environment,” said a California health department official.

A portion of Paicenes Ranch was leased by Mission Organics, a company using organic production practices and products in a transition-to-organics program. While not implemented, pelletized, heat-treated, composted chicken manure was used in the production process on that field, the only field on which manure was the major fertilizer.

Samples testing positive for E. coli O157:H7 were also found on the Eade Ranch, where the company Braga Ranch was growing spinach; on the Wickstrom Ranch; and on the Taix Ranch in places next to the Nyland Ranch, which had a 3,500-head cattle feedlot a half-mile away.

The conclusion: Growers of leafy greens need to zealously apply Good Agricultural Practices.
Risky practices include using potentially contaminated river or pond water, or possibly water from ungrouted wells; allowing wild animals – including birds as well as pigs, deer and small mammals – access to production fields or the water used to irrigate them; keeping livestock close to production fields or allowing their manure to contaminate water; and, possibly, letting workers with potentially contaminated footwear and clothing work in the harvest.

Investigators were able to pinpoint one field and one farm from which the tainted spinach came. Sophisticated laboratory procedures using genetic fingerprinting tracked a single isolate of E. coli from the stomachs of sick people back to a single field -– tracing backward through 13 bags of spinach found in refrigerators containing product codes that carried them to the processor and then the grower.

At the plant, they were able to identify four producers who had supplied spinach the day, Aug. 15, when Dole Baby Spinach, with product code number P227A, was bagged at the Natural Selections Foods South Facility in San Juan Bautista. Four ranches delivered spinach that day. From there, one offending field on one ranch was identified as the source.

But samples of soil, water and animal manure from all four farms contained E. coli O157:H7. And the fields on all four farms may not be used for production of leafy greens until remediation takes place, according to regulators. Remediation steps were not identified.

The investigators were not able to determine whether the bacteria were on or in the spinach – a key question. Whether the bacteria was deposited or splashed onto the spinach or taken up through the roots from contaminated soil or water was not determined. But apparently, the potentially deadly strain is more widespread in the environment than previously believed.

While many criticized the final report as adding “nothing new,” that was a point of pride for the government spokespersons, who said everyone “was informed in real time of the findings of our investigation,” and that growers and processors were able to adjust their practices before the final report was issued.

The 50-page report was released March 21, followed by a telephone press conference that drew 125 reporters and featured David Acheson, chief medical officer, Center for Food Safety and Applied Nutrition, FDA; Steve Solomon, deputy director, Office of Regional Operations, FDA; Mark Horton, California Public Health Officer; Kevin Reilly, deputy director, Prevention Services, California Department of Health Services (CDHS); Jeff Farrar, Chief, Food and Drug Branch, CDHS; and Mike Bowman, Office of Public Affairs, CDHS.

The report identified and confirmed the players and processes.

The inquiry was conducted by the California Food Emergency Response Team (CalFERT), a team of experts from FDA’s district office in San Francisco and the California Department of Health Services. The team was assisted by experts from the Centers for Disease Control and Prevention (CDC) and USDA’s Animal and Plant Health Inspection Service.

“The probe was a notable effort by federal, state and local officials,” said Robert E. Brackett, director of FDA’s Center for Food Safety and Applied Nutrition. “It yielded valuable information we can use to determine how best to reduce the likelihood of similar outbreaks.”

Potential environmental risk factors for E. coli O157:H7 contamination at or near the field included the presence of wild pigs, the proximity of irrigation wells used to grow produce for ready-to-eat packaging, and surface waterways exposed to feces from cattle and wildlife.

The precise means by which the bacteria spread to the spinach remain unknown.

“Where animals exist, there is E. coli,” Reilly said.

“It is in the environment,” Acheson said. “We don’t know enough about its ecology – how it’s replicating and how it’s vectored to leafy greens.”

“Since June 2004, USDA Agricultural Research Service working with CDHS has documented extensive periodic E. coli O157:H7 contamination in waterways in the greater Salinas Valley, though none of the isolates collected from these studies matched the spinach-associated outbreak strain,” Reilly said. “The Salinas Valley appears to have seasonal, systemic E. coli O157:H7 contamination in the environment.”

FDA continues to work closely with its federal, state and local partners to keep produce safe from bacterial contamination, Acheson said. Last August, the agency announced an initiative called “Leafy Greens” that focuses attention on the produce, contamination agents and other areas of potential public health concern associated with such products.

FDA recently issued a draft final guidance, “Guide to Minimize Microbial Food Safety Hazards of Fresh-cut Fruits and Vegetables,” which recommends measures to prevent microbial contamination during the processing of fresh-cut produce.

The report on the probe of the Dole spinach contamination, titled “Investigation of an Escherichia coli O157:H7 Outbreak Associated with Dole Pre-Packaged Spinach,” is posted at www.DHS.ca.gov.



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