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Pundit Special Science Report:

Part 1 — Food Safety Vulnerabilities In Yuma And Salinas

Jim Prevor’s Perishable Pundit, December 15, 2006

What do we really know about E. coli and the growing end of the business?

With everyone currently focused on green onions, it is worth noting that we do not fully understand the cause of the spinach/E. coli outbreak. There was a lot of attention paid to Salinas and possible problems with that growing area.

Now that production has shifted to Yuma, we wanted to assess the vulnerabilities in the region and visit with academic researchers in Yuma as well as Salinas working to understand the horticultural roots of foodborne illness outbreaks. To kick off the effort, Pundit Investigator and Special Projects Editor, Mira Slott, spoke to Jorge Fonseca of the Yuma Ag Extension Service:

Jorge Fonseca, Post-Harvest Specialist at the University of Arizona, Yuma Agriculture Extension Service. Learn more information here.

Q: Now that Salinas spinach production has transitioned to Yuma, will it be safer, less safe?

A: If we knew for sure the cause of the spinach/E.coli problem in Salinas, we’d all be much better off, but we don’t. The FDA discovery of a matching strain in samples from cattle feces, wild pigs and a nearby stream provide more pieces to the puzzle. But it still raises questions on the vector or vectors that transmitted the pathogens and on how the problem became so widespread.

There are still many unanswered questions. Regardless, we need to examine all possibilities and look at different areas where potential foodborne illness could occur in order to take effective actions. There are distinct differences in growing conditions between Salinas and Yuma that could play a role.

Q: Acknowledging that these differences may not be related to the problem, what would those be? And could they apply to leafy greens in general?

A: An overwhelmingly high percentage of the outbreaks associated with produce have occurred in July, August, September, and October, which happens to be the months when Salinas is harvesting leafy vegetables. We start harvesting in November. You won’t find a history of outbreaks with leafy vegetables in Arizona.

Q: Are you suggesting there could be a link based on weather conditions?

A: No one knows the cause of the outbreaks, but we need to examine all the possible reasons. In relation to this outbreak, I was in Salinas visiting suspected farms, and I went back and looked at weather conditions in those three or four different counties. The humidity in these areas is much greater than in Yuma, at least 15 to 20 percent higher.

Another thing… you always think Arizona is a very hot place, but if you want to compare harvest seasons in Salinas and Yuma, the Southwest part of Arizona, the temperature is much lower in Yuma. Sometimes it will be 10 to 20 degrees higher in Salinas. That may also be a factor. In Salinas, you have crops in higher humidity and soil in higher temps.

In fact, one problem we have in Yuma is ice on the leaves in December and January, which you normally wouldn’t have.

Q: Are there other contrasts between the two growing regions?

A: The water. Almost 100 percent of growers inYuma get their water from the Colorado river. In Salinas, most growers take water from wells. A practice of transferring that water to reservoirs is quite common because they need the pressure.

Q: What about irrigation techniques?

A: Irrigation in Salinas is basically with overhead sprinklers. In Arizona, 90 percent of growers use furrow irrigation for winter vegetable production. However, most of that furrow irrigation is used to grow head lettuce, as well as some Romaine and other small bed crop production. It is important to note that spinach grown here on large beds would also use overhead sprinklers similar to Salinas methods.

Q: Does the irrigation method play a part in food safety?

A: If there is a pathogen in the water, the food safety risk is higher if irrigating with overhead sprinklers, because it is easier for a bacteria to get attached to the leaves. The bacteria can hide in the stomata. It can attach to the pores in the leaves. If it’s too hot, the plant closes the stomata. If it gets colder in the evening, it opens up. Even during the day sprinklers stimulate the stomata to open, or bacteria could hide in cracks of leaves. If something goes wrong with the water, there is a much higher risk with overhead sprinkles.

Q: Are there advantages to overhead irrigation?

A: Yes. You can grow more plants per acre, for example. Ironically, some growers in Arizona are thinking of putting in overhead sprinklers. Another thing worth noting is that we have so much salt in Yuma that growers usually flood the field to wash it out before planting leafy vegetables.

Q: So the spinach outbreak problem may be unrelated to the differences in the weather conditions as well as the water and irrigation techniques?

A: That’s true. Many times it’s cross contamination from meat, or somewhere in the handling. An important discussion to bring to the table is related to the fresh-cut industry. I do research with the fresh-cut industry, which is the fastest growing food segment, and we definitely need to have all the companies sampling product daily to know microbial quality is OK.

Q: Do you know of any companies that have done such testing?

A: On the east coast, there are some smaller companies, like McEntire Produce in Columbia, South Carolina, that test daily for bacterial indicators, exploring the product and waiting to ship when they don’t see anything wrong. McEntire Produce was a pioneer in more comprehensive food safety testing. I know, because in 1998 as a graduate student, I was involved in taking product samples out of the packing line to test for pathogens.

I don’t think this is happening in some of larger companies. It’s hard for a company sourcing from nine farms to sample from all those farms daily. But to alleviate food safety risks, they have to implement a solution where they actually sample product before they ship it out. Issues do arise with sampling because you have to test a huge number of products for the tests to be statistically valid. And of course, you can never be sure that contaminated product doesn’t slip through the system.

Q: What about differences in topography between Salinas and Yuma?

A: One very important contrast: you see in some places in Salinas leafy vegetables in the valley, and another crop right next to it on a foothill, then a buffer area where you don’t grow anything, and then at the top of the hill, there is sometimes a cattle farm.

Q: And there is no scenario in Arizona where such proximity exists between vegetable production and livestock?

A: Nowhere to that extent. There is only one place in Arizona I can think of where you can find cattle and produce in the same area, and it’s still not that close in proximity. But I’m not saying that’s the reason why Arizona spinach production has been free of the outbreaks that Salinas has faced. We still don’t know the causes, and that’s why we need to continue researching.

Q: Do you have research projects underway to help uncover the underlying causes?

A: We are undertaking an irrigation study funded by a grant from the Arizona Iceberg Lettuce Research Council. We will be monitoring irrigation water in the Yuma Valley for three years. At the same time, we will be taking samples in different areas, counting birds, insects, and other animals, keeping track of wind, rain, relative humidity and temperature, to see if and how any of these factors correlate with peaks in microbials. We don’t know what is causing the outbreaks, but research studies like these will help us get closer to finding out.

So Jorge Fonseca believes in product testing and reassures us that Yuma doesn’t have the history of problems that the Salinas Valley has when it comes to food safety. What he can’t tell us is why. He lays out a few hypotheses:

  1. Humidity during growing season in Salinas is 15 to 20% higher than what it is during growing season in Yuma.
  2. The temperature is cooler in Yuma, growing season to growing season.
  3. Water comes from the Colorado River in Yuma versus wells in Salinas. And an implication that transferring water to reservoirs might be an issue.
  4. Irrigation is done mostly with overhead sprinklers in Salinas versus mostly furrow irrigation in Yuma.
  5. Topography is such that cattle operations are closer to vegetable growing areas in Salinas than in Yuma.

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