Paula Rivadeneira, Ph.D. is a Food Safety and Wildlife Extension Specialist, serving the entire southwest region of the United States. She is responsible for research, education, and outreach regarding all aspects of food safety and wildlife, which are both encompassed under the umbrella of One Health. Her specific programs include providing assistance and recommendations related to food safety and wildlife issues for 1) large commercial fresh produce growers, 2) small direct-market produce growers, and 3) school, community, and backyard gardeners.

Dr. Rivadeneira’s main goal is to assist fresh produce growers in excluding wild and domestic animals from their fields and gardens to prevent potential fecal pathogen contamination of fresh produce crops. Her lab focuses on microbiological testing of plants, soil, compost, water, air, and animal feces to identify the presence of foodborne pathogens.

Keeping Arizona families and farmers in the know, Dr. Rivadeneira maintains an active Twitter account @PaulaThePoopDr to quickly disseminate information, and she conducts presentations at numerous local, regional, and national professional meetings and conferences for growers, master gardeners, food safety personnel, and pesticide applicators in Arizona, southern California, and throughout the U.S.

Her current research focuses on developing fresh produce safety regulations for small farmers, conducting microbiological testing on air samples near fresh produce fields that are located near animal and compost operations, and working with County officials by testing for mosquito-borne pathogens that could impact our community. She is also working on a long-term study examining the risks that specific wildlife species pose to food safety, which will ultimately allow growers to prioritize their deterrents and increase the co-management of agriculture and wildlife.

As a result, she’s the doctor we need to see as it relates to the recent E. coli outbreak that took place in Yuma, Arizona this last spring. While the outbreak was recently declared over, Yuma farmers, the community, and food safety experts are still pondering the ramifications and long-term impact, especially since the official “point source” has not been found as this article goes to print.

Arizona Agriculture: Dr. Rivadeneira, they call you the “Poop Dr.” for a reason. Explain.

Dr. Rivadeneira: I am a Wildlife Biologist who entered the Food Safety world five years ago as a postdoctoral researcher at U.C. Davis working under my mentor, Dr. Michele Jay-Russell. Because my expertise is in wildlife, the majority of my food-safety work with the University of Arizona Cooperative Extension focuses on the interaction between animals and agriculture, particularly fresh produce.

One important way that fresh produce becomes contaminated with foodborne pathogens, like Salmonella and E. coli, is through poop. Fecal material harbors all kinds of bacteria. So, in my lab at the Yuma Agricultural Center, which is part of the University of Arizona Cooperative Extension, one of the many things we do is pathogen testing, and more often than not, we test poop. If a fresh produce grower has fecal material in or around their field, and they want to know if it has foodborne pathogens in it, they can bring it to my lab for testing. I also encourage anyone in Yuma and the surrounding areas who find fresh poop or a freshly dead animal to contact me so I can collect the poop and test it as part of a surveillance study I have been conducting since I started working for the University of Arizona. I don’t have funding for the project, but I think it’s very important to start to determine which species of animals pose the most risk to our fresh produce fields, especially in light of the recent E. coli outbreak in romaine lettuce that was grown in Yuma. So, my staff and I collect the poop and process it, we put it in the freezer, and someday I hope to get funding to develop an extensive database of Yuma wildlife and their poop, which will ultimately help our growers to assess wildlife risks!

Arizona Agriculture: Explain the virulent nature of E. coli from a science perspective.

Dr. Rivadeneira: All warm-blooded animals have the potential to carry E. coli in their guts, particularly ruminants, like cows and sheep. In fact, humans carry E. coli as well! But the E. coli in our guts generally does not make us sick – it’s an important part of our gastrointestinal flora that prevents harmful bacteria from taking over. There are actually hundreds of kinds of E. coli, and only some are pathogenic (harmful). There is a particular group of E. coli called Shiga toxin-producing E. coli (STEC), and they release Shiga toxin, which is considered a bioterrorist agent. It kills red blood cells, which then clog the kidneys while the kidneys attempt to filter them out, and this eventually causes hemolytic uremic syndrome (HUS), often times making the infection deadly.

Arizona Agriculture: Should the federal agencies have a better way of tracking or monitoring E. coli and any other foodborne diseases?

Dr. Rivadeneira: Like many other pathogens, E. coli is a reportable disease. So, if you go to the doctor or a hospital, and they find that you test positive for E. coli, they are required to report that to the Centers for Disease Control (CDC). Many infections are hugely underestimated because let’s face it, most of us don’t go to the doctor if we are vomiting or have diarrhea. We wait to see if it passes. It has to be really bad for us to go see a doctor. And since many illnesses are self-limiting, especially when you are a healthy adult, they work themselves out over a period of time, so you never see a doctor and you never receive an actual diagnosis. Basically, without forcing every person who has diarrhea to poop in a cup for testing, there may be no better way to track foodborne illness than the current method.


Dr. Rivadeneira says, “I just hope everyone remembers that the actual source of the recent E. coli outbreak has not yet been definitively found, and this fall when we start leafy greens production again, farmers will be doing everything they have always done to keep leafy greens safe, plus taking additional precautions.”

But let’s talk about traceback, which is the process of figuring out which foods people ate in the weeks prior to being confirmed that they have E. coli or another foodborne illness and tracing that food back through its life to its source. Everyone in the farm-to-fork continuum is supposed to keep documentation for one-step back and one-step forward, meaning that they know who they received the product from and they know who they gave it to. As a result, you should be able to ask a person what brand of lettuce they ate on a particular date and which store they purchased it from, and you should be able to trace the lettuce back to its origin, thereby identifying every company that touched the produce along the way, including the grower, harvester, processor, shipper, distributor, supermarket, etc.

During the latest E. coli outbreak, there seemed to be some confusion about what happened with product after it arrived at some of the processors. The reason for this is that lettuce and other vegetables from different fields often get combined to make mixed bagged salads, and it is possible to lose track of each crop at that point. So, in that regard, there are some points along the supply chain where improvements could be made for traceback purposes.

Arizona Agriculture: You’ve been studying migratory bird patterns and wildlife in general. Will there be future technologies to help us better protect against animal droppings found in fields? Or, will this be the ongoing challenge?

Dr. Rivadeneira: Here in Arizona, the vast majority of our fresh produce is grown in open airfields, and many, like those in Yuma, also have open irrigation sources in the form of canals that provide fresh water from the Colorado River. It’s a huge feat to prevent animal intrusion, but our farmers do everything they can to keep the produce safe. They use visual, auditory, olfactory, reproductive, tactile, and lethal deterrents, as well as natural deterrents like falconry. Recently, people have been proposing the use of technology like autonomous drones to protect fresh produce fields, but that is not currently an economically feasible option.

The one thing we know for sure is that there is no one solution to the issue of animal intrusion so we are looking toward the principles of Integrated Pest Management to help us. I have recently been working with a grower in Mexico who has implemented some simple but highly effective habitat enhancement techniques. He has demonstrated amazing results by simply improving the wild habitat surrounding his fields. In the past 2 years since he started the improvements, he has significantly decreased animal intrusion into his fields to almost zero, and he has decreased his use of pesticides in some fields by 70%. I am eager to find growers here in Arizona who will allow me to implement the same practices locally!

While technology is great and can surely contribute to many aspects of farming, I think the best way to manage nature is by using nature to our advantage through habitat enhancement, ecosystem development, and establishment and protection of ecological corridors. Wildlife will be an ongoing challenge for our growers, but I do not believe that it is insurmountable. We just need to think outside the box by incorporating Integrated Pest Management methodologies, and I think we will find much better ways to manage wildlife than what we are currently using.

Arizona Agriculture: The farmers initiated the Arizona Leafy Greens Marketing Agreement (LGMA) and now we have the federal Food Safety Modernization Act (FSMA) that in Arizona is enforced through the Arizona Department of Agriculture under FSMA’s Produce Safety Rule. FSMA took much of its standards from LGMA, though it’s relatively basic compared to the more robust standards of LGMA. What else can our farmers be pushing the federal government to change/improve or drive to protect consumers?

Dr. Rivadeneira: I think our farmers consistently go above and beyond to protect consumers. Arizona (and California) farmers lead the nation in food safety with worker health and hygiene training, water testing, animal deterrents, use of certified biological soil amendments, pre-harvest pathogen testing, auditing, and documentation. Since my work focuses on pre-harvest food safety, I do not know as much about what happens after the crop leaves the field, but from what I understand, it doesn’t appear that the rest of the farm-to-fork continuum is regulated in terms of food safety as strictly as farmers are regulated. In addition, I think end users, including restaurants and actual consumers, have to take responsibility for themselves once fresh produce arrives in their own kitchen. Every one of us chooses to take risks every day. We leave our home, get into a vehicle, buckle up, and drive away. We know we could get into an accident, we know we could die. But we get in the car anyway, and we do everything we can to keep ourselves safe. There are so many aspects of our lives in which we accept a certain level of risk, but for some reason, people do not accept the same risk and implement the same precautions when it comes to their food. It is unreasonable to think that there is zero risk in eating fresh foods that are grown outdoors, that require specific temperatures to remain fresh, that are handled by numerous people, and that are potentially transported long distances. If you are putting something in your body that you are preparing in your own kitchen, regardless of where it originally came from or what it is (meat, vegetables, legumes, etc.), I believe you need to take responsibility to know that it is safe to eat. If you run a restaurant, the last thing you want is for your customers to become sick so the final responsibility lies on you and your staff. If you are the last person to handle food before it goes in someone’s mouth, including your own mouth, then you have final responsibility in making sure it’s safe.

So, to answer the question about what farmers should do to get the government to better protect consumers, I would say that farmers have done and continue to do an amazing job at maintaining the highest food safety standards, and that’s what they should continue to focus on. If farmers are expected to fight for consumer safety, then shippers, processors, harvesters, restaurants, and everyone else involved in the farm-to-fork continuum should have to do that too. I find it baffling why so much falls on the shoulders of the farmers when it comes to food safety. That’s where it starts, but that is certainly not where it should end. Feeding our country is a group effort, and the best way to protect consumers is for each player to maintain the highest standards regarding their own responsibilities.

Arizona Agriculture: Are growers regularly going to you and other scientists to learn more and apply technology?

Dr. Rivadeneira: I feel like most growers in the Yuma area know that the University of Arizona Cooperative Extension is here to help them. As an Extension Specialist, my only job is to help growers with food safety concerns. My research is always based on their needs, and the outcomes from my research are designed to give them solutions, or at least options. There are a handful of farmers who I meet with regularly, and we explore current and upcoming issues so I can know what kinds of grants to apply for and what kinds of research are needed.

Most fresh produce growers are pretty savvy when it comes to science and technology, so they are open to research and to try new techniques and methods, even those that I present to them that are considered a little outside the box. During the recent E. coli outbreak, the industry reached out to us at Cooperative Extension for expertise and assistance in identifying the source of the E. coli contamination, and to examine a number of variables, including weather-related concerns. They know that we conduct unbiased research, and will do our best to give them answers. In addition, working groups have been formed to seek out the root cause of the outbreak, including the Leafy Greens Task Force and the Desert Food Safety Consortium. The Task Force includes people from industry, research, and regulatory agencies, and includes sub-working groups to cover specific areas of concern related to the outbreak.

Arizona Agriculture: Do you see value in FDA’s decision to name a farmer related to the recent E. coli outbreak in romaine, and not name a shipper or distribution network that consumers might recognize? 

Dr. Rivadeneira: In my opinion, it was not appropriate for FDA to name a single farm during the recent E. coli outbreak since they could not identify exactly where and when the lettuce was contaminated. They reported the name of the farm who simply grew the lettuce, which seems pointless because it does not benefit public health in any way. Since that’s the case, it seems odd that they didn’t name everyone involved in the entire distribution network. The public read the update on the FDA and CDC websites identifying the farm who grew the lettuce, or they heard it on the news or read it in the newspaper, and that name stuck in their heads. It didn’t matter that the next sentence stated that they couldn’t determine if the contamination happened on the farm and they couldn’t pinpoint where the contamination actually occurred. The damage was done. The farm they named is one that not only participates fully in the implementation of food safety practices, but they are a leader in food safety in Yuma, actively participating in a leadership role on the Yuma Safe Produce Council, and maintaining exemplary records of their food safety efforts. So, I find it frustrating that they would name any individual farm.   

Arizona Agriculture: You said something to me the other day at a “Foodie” forum that I thought was meaningful. “Our U.S. farmers are daily feeding millions.” Please expound on this point?

Dr. Rivadeneira: During our peak growing season, approximately 1,000 to 1,200 trucks transport leafy greens out of Yuma on a daily basis. I can’t even grasp the total number of people who eat fresh leafy greens from Yuma from November through March every year. Despite this astronomical number, we have only had one foodborne outbreak traced back to Yuma’s leafy greens, and the source was never confirmed. Did we grow lettuce in Yuma that was identified as a potential source in the recent E. coli outbreak? Yes. Did it get contaminated while it was in the field or at any point while it was in Yuma? No one knows. While the FDA claims to have found the same E. coli strain in a canal that provides irrigation water to Yuma agricultural fields as was identified in the outbreak, that still doesn’t tell us the source. The water did not contaminate itself.

With the millions of pounds of leafy greens that our farmers supply to people across the nation, I think it’s pretty miraculous that not a single outbreak has been confirmed to come from Yuma. It’s tragic that people recently got sick from lettuce that was grown here. I know how painful it is to have a serious foodborne illness. I had Salmonella in 1986. I was hospitalized with my organs failing, and I remember that the pain was so bad that I didn’t want to live. I suffered for 20 years with residual issues related to that infection. I say that not for sympathy, but so that people will know that I genuinely understand the physical and emotional pain associated with foodborne illness. I just hope that everyone remembers that the actual source of the recent E. coli outbreak has not yet been definitively found, and this fall when we start leafy greens production again, farmers will be doing everything they have always done to keep leafy greens safe, plus taking additional precautions. The majority of our growers, despite the fact that they are large commercial farms, are owned by families who are involved with every aspect of production often feeding their own product to their own families. They are real people who care about what happens to the people who consume the food they grow. They take pride in their work and in their efforts to provide safe fresh produce to our country. I hope that consumers will not let this incident change their view of Yuma growers who have always grown the best winter vegetables in the country!

Arizona Agriculture: From the perspective of a scientist, what else could we be communicating to the public?

Dr. Rivadeneira: It’s important for the public to know that growers are doing everything they can to help find the root cause of the outbreak. I have been interviewed by several media outlets asking if growers are playing any role in the outbreak investigation. I think the public wants to know where growers stand, what role they are playing, and what they are doing in anticipation of our upcoming leafy greens season. There is always a question of how much transparency is good or effective during an outbreak, and that will have to be something that each grower decides for him/herself. But the public wants to know that growers are protecting them and their families so I think sharing that information is critical.  

Arizona Agriculture: Does science show that E. coli carried in the water, then absorbed into the soil and taken up by the plant could cause E. coli to be present in the plant?

Dr. RivadeneiraMy understanding from other UA agricultural experts is that it is unlikely that E. coli from irrigation water is taken up in the roots of plants, resulting in the contamination of plant tissue. The concern with having E. coli O157 in irrigation water is that it could touch the edible portion of the plant, possibly through overhead irrigation, and that could potentially cause contamination. There are many other variables that could also result in E. coli contacting and/or surviving on plant tissue, including wind, temperature, the presence of animals, etc.

Arizona Agriculture: If E. coli is confirmed in the canals, why have we not had a rash of outbreaks in Yuma and elsewhere? If it’s that pervasive in the water (which is not yet confirmed with all scientific certainty), where’s the data to support a widespread problem?

Dr. Rivadeneira:  My colleague, Dr. Channah Rock, who is a Water Quality Specialist with the University of Arizona Cooperative Extension, is better suited to answer this question, but I will give you my take on it. The recent outbreak of E. coli O157 was tragic, and everyone is working very hard to find the root cause of the contamination. Based on testing results from the FDA, people are concerned that there is E. coli O157 in the canal water that growers use to irrigate crops. Growers test for generic E. coli in irrigation water frequently during the growing season, but generic E. coli tests do not directly test for E. coli O157, which is the pathogenic E. coli related to the recent outbreak. So, it is certainly possible that E. coli O157 has gone undetected in canal water.

But as you mentioned, why have we not had an issue with it until now? Well, there are a couple of things to consider. First, the samples that the FDA collected that tested positive for E. coli O157 were huge! Their samples were 50L (liters) compared to the 100mL (milliliters) that are usually collected. That means they collected 500 times the normal sample size! It’s like comparing a bottle cap full of water (normal sample size) to a bathtub full of water (FDA sample size)! This tells us that the prevalence of E. coli O157 in the canal water is probably pretty low since it took such a large sample to be able to find it. With such low levels, a combination of natural die-off in the environment and our standard measures for ensuring produce safety probably protected consumers. Secondly, we don’t know where in the canal the positive samples were collected so it could be confined to a specific area, which would limit exposure. And third, growers go to great pains to ensure that fresh produce leaving their fields is safe by following, and often going beyond all the rules and regulations placed on them by the Leafy Greens Marketing Agreement and the Food Safety Modernization Act.

Farmers monitor and maintain their fields, train their workers, and conduct extensive testing so that any potentially contaminated produce never leaves the field. While I don’t know if we will ever find the root cause of the recent E. coli outbreak, growers are already preparing to implement whatever corrective actions they believe will help to further protect the crops. Much more environmental sampling, potentially over the long term, will need to be conducted to search for answers. I hope that industry will depend on me and other experts at the University of Arizona to conduct sound science that will give them potential answers to this outbreak.

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