Investigators continue their tedious search for the source of the E. coli that apparently contaminated romaine lettuce, causing this spring’s deadly outbreak. But it’s becoming increasingly unlikely they will find a smoking gun.
The human toll so far, including one person in California who died, is 132 confirmed cases, 72 hospitalizations, and 20 people with hemolytic uremic syndrome, a type of kidney failure, according to the Centers for Disease and Prevention.
Epidemiologists from the CDC are working closely with investigators from states and the U.S. Food and Drug Administration. They are all trying to find common denominators among victims and entities along the farm-to-fork supply chain that will help pinpoint the source of the dangerous E. coli O157: H7 bacteria.
So far the closest they have come is the general region around Yuma, AZ, where most of U.S. romaine is grown from November through March. New illnesses have dropped to almost zero since the harvest wrapped up in Yuma and moved north to California fields.
“Our traceback investigation is still very much ongoing and we are continuing to examine the full supply chain and dozens of growers, mentioned previously. I would reinforce one of the messages from our last update, which is that no single grower, distributor, or processor is able to explain the entirety of this outbreak,” an FDA spokesperson said Tuesday.
Two primary factors contributing to the difficulty of the traceback have to do with the way leafy greens are processed and how they are labeled, according to one microbiologist who helped with the investigation into the deadly 2006 E. coli outbreak traced to fresh spinach.
Michele Jay-Russell said the common practice of commingling leafy greens from multiple growers during washing and chopping in processing facilities can easily lead to widespread contamination across multiple finished products. That wasn’t really a factor in the 2006 spinach outbreak, though, according to Jay-Russell, who is now research microbiologist and manager for the Western Center for Food Safety at the University of California-Davis.
In the 2006 spinach outbreak, enhanced labeling that went beyond that required by federal law, also helped investigators to quickly narrow the implicated spinach to four growing fields. A few days later they found the specific spinach field where the contamination had occurred. Wild pigs had invaded the field and their feces contained the deadly bacteria. The outbreak strain was also found in manure from a cattle feedlot.
“In 2006 we had a lot code (on spinach package labels) that sent us to Natural Selections’ fields and then we narrowed it to one of them,” Jay-Russell said Tuesday.
“Compared to 2006, this is obviously a lot more challenging. To me, the traceability is what’s hampering this investigation. The whole question is why is this traceback so complicated?”
Federal law only requires entities in the food supply chain to keep track of shipping and receiving one step forward and one step back.
Processors, for example, don’t have to know who grew the romaine lettuce they are washing and chopping if another company initially bought it from the grower. They also don’t have to keep track of all the links in the chain after the chopped lettuce leaves their factories. There are usually multiple entities between processors and the restaurants or retailers who sell food to consumers.
The fresh produce industry tried to address the traceability tangle after the 2006 spinach outbreak by launching the Produce Traceability Initiative. The voluntary labeling system has been praised by food safety experts, governmental entities and consumer groups. But many growers and other entities in the supply chain have not implemented the labeling, usually citing increased costs.
Pigs, birds, poop, and dirt
Outbreak investigations usually involve testing of products, equipment, facilities, fields, irrigation and wash water. Investigators also look at the lay of the land, literally, to see if there are any obvious sources of pathogens up a hill from growing fields, Jay-Russell said. Investigators test soil samples, too, but with E. coli bacteria there is a relatively small window of opportunity to find anything.
“In 2006 we tested the soil, but we didn’t find it (the outbreak strain of E. coli),” Jay-Russell said.
“The field had been tilled and it had been baking in the sun. E. coli isn’t as resilient as Salmonella, for example, and it usually doesn’t survive those kinds of conditions.”
One place E. coli can survive comfortably is a feedlot, Jay-Russell said.
Cattle and other livestock shed the bacteria in their feces. Pathogens such as E. coli easily become airborne via dust in feedlots, eventually landing in growing fields. Jay-Russell said researchers in Nebraska found bacteria well beyond the 400-foot setback that some produce associations require for their grower members.
In the Yuma area, some growers have voluntarily gone to one-mile setbacks, she said.
“The growers in the Yuma are very aware of potential issues with CAFOs (concentrated animal feeding operations),” said Jay-Russell, who worked with agricultural animals in Arizona’s Imperial Valley when she was a full-time veterinarian.
“There is a much higher density of cattle in the Yuma area than in Salinas Valley where so much of the California leafy greens are grown. In Salinas, there are mostly cow-calf operations … you see them grazing on the hillsides.”
Salinas-area produce growers also have the benefit of Mother Nature’s clock. The rainy season that can send runoff from grazing areas into growing fields hits during the offseason, Jay-Russell said. Also, there is virtually no danger of manure drift from grazing areas.
Runoff and manure drift from agriculture animal operations can be mitigated to varying degrees, but wildlife is another story, Jay-Russell said.
In the Yuma area wild pigs, known as javelinas, are native — and aggressive when it comes to finding tasty crops and irrigation water. Fencing does little to stop the pigs, or deer and other wildlife when it comes to a field of fresh produce.
Even if fences could keep out wild animals, they can’t keep birds out, and that is a big problem for growers in Arizona.
“We’re in the Pacific Flyway out here and that means huge numbers of birds coming through,” Jay-Russell said. “It’s a numbers game when birds are involved. A single bird isn’t a problem.”
The Audubon Society estimates 1 billion migrating birds use the Pacific Flyway every year.
The migrating birds, as well as resident flocks of crows and other birds, can’t pass up the easy pickings of animal feedlots, Jay-Russell said. And while many people don’t think birds carry E. coli, researchers from UC-Davis report E. coli has been found in the feces of multiple avian species.
A current research project underway at the University of Arizona that is exploring the use of raptors to help keep birds and rodents out of produce fields has also highlighted the E. coli dangers from avian sources.
“You can try to scare the birds away from feedlots, but they get used to the noises and just come back,” Jay-Russell said, adding that resident flocks are particularly difficult to trick with flashing lights and noisemakers.
“They knew when the feed is going to be put out and they show up. Then they fly to the (produce) fields seeking water. They can contaminate the food, the dirt and irrigation water.”
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