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Reporting on science, technology and innovation in Arizona and the Southwest through a collaboration from Arizona NPR member stations. This project is funded in part by the Corporation for Public Broadcasting.Additional stories from the Arizona Science Desk are posted at our collaborating station, KJZZ:

Yuma Ag: What Carries Food-Borne Pathogens and How Far Do They Spread?

Efforts to protect the country's agricultural crops from pathogens and other threats requires some unusual practices.  Maya Springhawk Robnett of the Arizona Science Desk reports from the fields of Yuma...

Ever think about flies and pathogens?

“A little fly lands on your coke and you’re like, ‘Oh, shoo away, fly!’ You have no idea what it left behind," says Dr. Paula Rivadeneira, "No idea.”

Rivadeneira has an unusual job. Her official title is extension specialist in food safety and wildlife at the Yuma Agricultural Center of the University of Arizona. She calls herself Paula the Poop Doctor. In food safety, feces are a common field contaminant.

<b>"A little fly lands on your coke and you're like, 'Oh, shoo away, fly!' You have <i>no idea</i> what it left behind. <i>No idea."</i></b>

“Pathogens are often associated with poop," says Rivadeneira, "and animal poop in particular!”

Rivadeneira and her research technician, Martha Ruedas, will set out fly traps as well as buckets of water to collect dust samples near Yuma fields. They want to know if individual instances of pathogens in the fields are the result of flies, dust blowing contaminants, or just wild or domestic animals. The researchers collect samples near agricultural areas on the outskirts of Yuma County.

Ruedas screws off the lid of a fly trap. It’s a container they fill with a special kind of bait. Do you catch more flies with honey or with something else?

“I’m preparing the trap with this solution that is egg fermented," Ruedas explains as she begins to pour the bait, "And we will see how many flies we get.”

The smell is not pleasant.

Yuma farmers get nervous when they see Rivadeneira in their fields. If she finds a single contaminated head of lettuce or other vegetable, the policy is to condemn an entire portion of that field.

“The growers all belong to this group called the Leafy Greens Marketing Agreement," Rivadeneira explains, "And one of the guidelines that they’re required to follow is if there is any kind of contamination in the field, a single positive hit, they’re not allowed to harvest anything around that area. You could lose acres and acres from just a couple of animals coming in overnight.”

Rivadeneira hopes her study will not only help determine where the pathogens come from. She wants to know whether the policy of condemning large areas around a single contaminated vegetable is really necessary.

Today she’s focused on fly traps and dust samples, but Paula the Poop Doctor can’t help herself.  Rivadeneira stops the moment she sees bird droppings in the dirt near a field and gets excited.

“You can never have enough ziplock bags," she says, kneeling down to the dirt.  "I’m gonna scoop the bird poop right here…”

"You can never have enough ziplock bags." -Paula the Poop Doctor

Farmers don’t like talking about food safety. But contamination is a major concern for growers because it not only hurts their bottom line; it also undermines consumer trust. This became a problem in September 2006 when California experienced an outbreak of E. coli in spinach crops.

Valentin Sierra, a food safety specialist for Amigo Farms in Yuma, says that changed the conversation, and the industry.

“A lot of growers and shippers were already doing some kind of food safety practices but it wasn’t really a focus then. But now, after that outbreak, it’s been one of the key focuses of agriculture business,” Sierra explains.

Food safety is more costly than it was before 2006. Even harvesting equipment is far more expensive than it used to be, because sanitation requirements call for many items to be made with stainless steel and thoroughly cleaned daily. And despite the loss of product and consequently, money, Sierra says it’s worth it to condemn a large portion of a field.

“Let’s just say you do find just one contaminated head," he says.  "Who’s to say that that head won’t contaminate the rest of the load? So, you’re already taking a step, why risk it?”

The Yuma Ag Center study is scheduled to conclude in March, when Rivadeneira’s team will run the lab samples and report the results to local growers.