- Our next speaker is Kathleen Glass. She is a distinguished scientist at the University of Wisconsin-Madison, working at the Food Research Institute. Kathleen is here to talk to us about Listeria, where do you look, and how to prevent it.  - Well thank you very much for the invitation. I am very pleased to be here. I'd like to preface this with my experience has been more with processed foods, with dairy, food products, as well as meat products, and when I started working with Listeria in the caramel apples about a year or so ago, never did I really anticipate that this was going to be a problem. It certainly has taken the entire produce industry by surprise, but what I think we need to do is understand a little bit more about where this bacterium comes from, and how we're going to be able to control it. So this is what we're going to be working on today, we'll be taking a look a little bit more of an overview of foodborne illness, so we can put this into perspective, and then drill down to specifically what Listeria monocytogenes is, how dangerous is it, where do we find it, how does it get onto our foods, and more importantly, how do we make sure that it's not going to be a problem in the future. So as we're going to be getting a look at the background for foodborne illness, we have to understand that about one in six individuals in the United States will come down with some type of foodborne illness every single year, so as you look around with this room, one in six of you, may have some form of illness that might be as simple as some nausea, diarrhea, vomiting, but in other cases can be become very severe that might cause hospitalization or even death. So as we look through this, fresh produce, and we're talking about leafy greens, tomatoes, cucumbers, sprouts, and even apples have become the leading category of foodborne illness in the United States. 

Sometimes that surprises individuals, but we have to keep in mind that fresh produce definitely does not have an additional kill step, such as cooking and pasteurization, so if the food product comes in with contamination, the simple sanitation that might occur may not be sufficient to make that food product completely safe, and so this provides us with some very unique challenges. Now specifically, what is Listeria monocytogenes? You probably did not hear about this more than a year ago, but it definitely has come on to the screen very much in the fresh produce industry in the last few years. Even though we have probably 48 million illnesses, of foodborne illnesses, in the United States every year, Listeria only accounts for about 1,600 of those. So you think of that as being a very minor illness. However, when we take a look at the number of people that die as a result of Listeria, it is one of the top three microbes that causes foodborne deaths. The illnesses that are associated with this can be very severe. It might first appear as being flu-like symptoms, fever, stiff neck, but it can progress into more severe illnesses such as meningitis, septicemia, and even death. About 90 to 100% of the individuals who come down with listeriosis will be hospitalized and about 20 to 30 of those percent of those individuals will die. Now not everybody is going to be at risk for contracting Listeria. There are certain categories of people who are, however, going to be susceptible, and those are people that are going to have poor immune systems. 

As we age, our immune system also ages, and we become more susceptible to it. Certainly, people that are older than 65, 70 years old are more susceptible, but even as we age to 50 and 60, our risk becomes higher. Now besides the elderly that are going to be at higher risk, pregnant women are going to be at higher risk, not because they have an immune system that's problematic, but at the placental area is going to be an area in which there's not going to be the same type of immunity in order for the woman not to reject the fetus. So this is going to be an area which Listeria can attack and then can cause problems, once again we'll just be like a flu-like symptoms for the mother, but potentially can cause still birth and then might infect the infant after it's born and can cause death in that place. People that have had transplants of organs, they're going to be on immunosuppressant drugs, people with cancer, chemotherapy, HIV/AIDS, and other autoimmune diseases become higher risk individuals, and even people that have diabetes are going to be at higher risk than the normal consumer. What is trickier about this, it takes a while after you consume the quantity of Listeria for it really to take over the body and to cause illness, so on average, it's about three to four weeks after you consume the Listeria before somebody becomes ill. Although there may be a range that it might be a shorter period of time or a longer period of time, three months, or three weeks, is pretty typical. So think back what you ate three to four weeks ago. Are you going to remember what was there? Is that food product going to be available for us to do testing to see whether or not that was really going to be the food product that was really the carrier of the Listeria? So as a result, it's very difficult to find the source of contamination, and it's also difficult then to try to prevent this from occurring in the future time. So where does Listeria come from? We said that you are going to eat it, and that's where it's going to get into your body and can cause illness, but it's going to come from the environment. 

So the best places for us to find Listeria are going to be in water, soils, it comes out of the animals and then once it is from those particular sources, it gets on to the raw commodity, so it gets on to the fresh produce, or it's going to get on to, into the milk, so once you have it on the top of the food, or it might come in on people's shoes or on tools or on conveyor belts, things like that, it can set up shop within a food processing environment, and you aren't going to see the Listeria on those areas within the food processing area, but as I said, it can get into the nooks and crannies, and if there's enough moisture in there, if there's going to be a nutrient source that left over from food debris, it is a great place for the Listeria to be able to grow and hang out for a long period of time. So we can have resident populations of Listeria in the food processing environment that you might go through a normal cleaning and sanitation, but you can't get into those nook and crannies very easily, you can't see the Listeria that's sitting on the surface, and as a result, if you can't see it, you may not necessarily be able to clean it and sanitize it properly. So as a result, it can be very difficult to remove. We have some pictures here, where you have some cattle that happen to be in an orchard, whether or not they should be, probably not, but even if you have Listeria that's setting up shop in that water that's going to be used potentially for irrigation, or if you might be pulling out some dropped apples and putting it into the bin, but you can also find it, once again, within the food processing environment on conveyor belts and drains and things such as that. So once again, what we want to do is take a look at the big picture. We don't want to get too hyperfocused just on fresh produce or on apples, although that is part of it, but what type of foods are going to be high risk? So if we look at things that have been associated with listeriosis in the past, a lot of them might be products, dairy products that were made with raw or unpasteurized milk, particularly soft cheeses, they're going to have high moisture, they aren't going to have a lot of acidity, and they may not have a lot of starter culture left in it, and as a result, the Listeria loves that type of environment and will start growing to high levels. If I am a susceptible consumer, and I eat a lot of that Listeria, I can potentially get sick. If there's just small levels of Listeria in there, I might be able to just pass it through my system and not have any problem, but soft cheeses are definitely one of those that can be contaminated and can support growth to levels that are going to be infectious. Other types of foods, we know that there's been listeriosis has been associated with smoked salmon, certain type of deli foods, processed meat products that don't have any preservatives in it, raw sprouts and other fresh produce have been associated with outbreaks before. Another tricky part about Listeria is that it can grow under refrigeration temperatures. 

So you think about putting foods in a refrigerator as a way in which you are going to be able to preserve them and keep them safe for long periods of time. But, our friend Listeria doesn't care about that. It might grow slower when it's at 45 degrees Fahrenheit, compared with at room temperature, but it'll still grow to levels that can then cause illness. It can also survive freezing, so about the only way in which you're going to be able to get rid of this is through cooking, pasteurization, and good cleaning and sanitation. Now if this is going to be such a problematic bug that we can find it in a lot of different products, in different types of environments, it grows under refrigeration temperatures, why don't we have a lot of people that get ill? And part of it has to be the fact that even though it's common, it may be at very low levels, and we want to keep them at low levels or non-existent levels. So food products that don't support growth, such as those things we would consider to be shelf stable, things that are dry, things that have a lot of acid in there, Listeria is not going to grow. It might survive for a period of time, but it's not going to grow. Those are low risk food products. On the other hand, food products such as refrigerated ones that have long shelf life, potentially can support growth of Listeria. So keep it from growing, that's going to be the number one thing. 

Keep it out of there. That'll be another option. But once we get into the food processing environment, a packing environment, what we need to do is bring in together all what we know about food safety and that includes having good manufacturing practices, good agriculture practices, cleaning, sanitation, good temperature control, and maybe even using some ingredients within our foods that have been used as growth inhibitors. So sometimes, even acid can keep the Listeria from growing. High salt concentration might be able to keep it from growing. So we put all of these things together, and you aren't necessarily going to have one stop shopping that you'll have one way in which you're going to keep the Listeria from growing, but we'll have to take a look at each particular food commodity, each food product, and find out what is going to be the best way in which we're going to be able to control it. Now, so we have low levels to begin with, we have food products that can be stable, we can keep it out of there, and the other thing is the fact that we have relatively a small number of consumers that are going to be susceptible. As I indicated earlier, people who are the elderly, the people who are on chemotherapy, HIV, AIDS, but they're really a small sub-population in the United States, but we have the bad news is that we have a growing population that are becoming older, with an older immune system, we have a growing number of individuals who are survivors of cancer and survivors of HIV, AIDS, and so we do have to be able to protect them whatever we can to make sure that we don't have Listeria on those food products. So when we're taking a look at listeriosis, as I said when I started actually 30 years ago at the Food Research Institute, the big concern with Listeria was going to be dairy products, particularly soft cheeses. The dairy industry made marvelous head ways in understanding which of their food products were higher risk and which ones were lower risk. 

They were make sure that they kept Listeria out of the environment, they did the pasteurization, and as a result, the number of cases of listeriosis dropped that were associated with dairy products. Then the meat industry found out through outbreaks that they had products that were susceptible, and so hot dogs and sliced turkey products that are deli products without growth inhibitors, they found out that that supported growth of Listeria, so they made changes in their processing, in addition of growth inhibitors, and as a result, we made great strides in reducing the number of cases of listeriosis associated with deli products. But what has come out now? We are now looking at what happens with fresh produce. Now this should not be as surprising as we think because if we take a look back through the literature, we find that there was a fairly large listeriosis outbreak back in the early 1980s in Canada, and what happened with this case is that there was a farmer that was fertilizing his cabbage field with sheep manure as a natural fertilizer. Well what they didn't pay attention was there were a couple of ducts of the sheep due to listeriosis and so obviously, that sheep manure was carrying Listeria. The Listeria came from the sheep manure onto the cabbage, they kept the cabbage in cold storage for long periods of time, as you do with cabbage, and then what they used, the cabbage was made into coleslaw, and that coleslaw had high levels of Listeria because it came in on the cabbage to begin with. Once again, susceptible consumers ate that cabbage, they came down with listeriosis, and they had 35 perinatal cases, so those were going to be the mother, infant pairs that were there. There were seven other adult cases that were there, and ultimately, about 30% of those individuals died from eating the contaminated coleslaw. As I said, we started focusing more than on dairy products and on meat products, but then, in 2011, we had an outbreak of listeriosis associated with cantaloupe, and in this particular case, there were 147 cases, including 33 deaths, once again a lot of people didn't anticipate that they would die from eating large amounts of cantaloupe. In this particular case and we'll talk about this as a case study on the next slide, they did have very poor practices in trying to control the dirt within the packing facility, and as a result, the individuals that had this particular packing facility are facing criminal charges because they had disregard for making sure that they had good practices. 

Now, more recently, and the reason why you're probably here listening about Listeria was the outbreak in the end of 2014, beginning of 2015, that were associated with caramel coated apples that were commercially produced, and once again, we'll talk a little bit more about these in details of how Listeria got onto those apples to begin with. 35 cases, including seven deaths. There were three individuals in the state of Wisconsin who also became ill, and we'll talk also this is unusual because in this particular case, we had three children that also were ill, and they were otherwise healthy, and they weren't considered to be high risk. And if you're paying any attention to the news, right now, there is an ongoing recall and an outbreak of Listeria due to prepackaged lettuce. This is also not only in the United States, but also in Canada, so far, these were updated as of Sunday, there were 19 sick and two deaths that were associated with eating pre-bagged lettuce with high levels of Listeria. So if we have Listeria that's coming in from the environment and all we're left with is not really a quick, a kill step on this, we don't cook it, we don't pasteurize it, what are we going to do with this? Well what we have to do is take a look at what happened wrong in the past. And one of the things we want to take a look at is the case study is in 2011 with the cantaloupe with Listeria. Now this particular outbreak, as I said, had 147 illnesses and 33 deaths, this affected people in many states in the United States, and what they found out through the investigation is that the same equipment that was used for handling the cantaloupe was also used to handle potatoes, and the potatoes came in dirty, and obviously cross-contaminated the handling equipment, and what happened then is that the Listeria that came in on the soil from the potatoes then got onto the skin of the cantaloupe, and you think about a cantaloupe, it's actually very porous. It's got that crackling netting on the outside, which is not impervious to penetration, and if you think about where you've got that stem area, it's very soft in there, so as they do some rough handling, the Listeria can penetrate into the inside of the cantaloupe, and it's now going to be in an environment where it's going to be a fairly neutral pH, it's not very acidic in a cantaloupe, it's going to be high in moisture, and think about where you are going to be buying the cantaloupe, it's going to be in these great big bins that are going to be sitting in the middle of your grocery store, you're going to take it home and might let it sit out on the counter top for a few days before you cut it, and then if you aren't going to use it all at one time, you might cut it, and put part of it in the refrigerator, and if you're refrigerator is not at the right temperature, it can also grow then. So it has great opportunities for being able to get into the part of the cantaloupe and also to be able to grow. 

As a result, it can get into high levels of Listeria. Once again, if you have a susceptible individual that eats this, they can get an infectious dose and can cause illness. So why wasn't there problems with other type of produce? Well the potatoes are typically cooked before you're going  to be eating it, which will kill the Listeria. Cantaloupe, unless somebody is doing something different around here, I personally don't cook my cantaloupe, and as a result, can eat the Listeria for that. Now, the second thing that we want to take a look at is in 2014, beginning of 2015, where the caramel apple outbreak. And as I said, we had about 35 cases including seven deaths, and there were cases that were in the state of Wisconsin, and what I said what was really unusual about this is that we had three otherwise healthy children that became ill. When we talked to our state epidemiologists about this, this was very very confusing with all of us because we thought of caramel apples as being a shelf stable food product, and why in the world would there be listeriosis with this because we didn't anticipate there being any growth. And if we're taking a look at Listeria, attacking the individual children, that was out of the realm of possibility too, and were were looking at potential superbug? And so we needed to start understanding a little bit more about what was going on with this. What they found out with the trace back is that all the caramel apples that were implicated with the illness were provided with the apples from a single apple packer, and this apple packer had those strains of Listeria throughout its environment. What we then found out is, once again, we were looking to see whether or not the Listeria could really grow on the caramel apples, and what we found out in there is that first of all, the apple sanitation that was being used was probably insufficient to be able to kill the Listeria that might be harboring in the stem and the calyx area of the apple. 

So it was there to begin with. So once again, you have to keep it out of there. The other thing is that once you make a caramel apple, you're going to put a stick in there. What happens when you put a stick into the middle of an apple? You have juice that comes out. The juice ends up getting caught between the surface of the apple and the caramel, and all of a sudden, you have a very moist environment, it's still going to be fairly neutral pH, it's a wonderful environment for the Listeria to grow in, and when you set them out at room temperatures got to be an area where it had a fairly high dose, and so if some child ate one, two, maybe three of those apples, they're going to have a slug of Listeria and can get ill. So where does this Listeria become a problem? As growers, you can have Listeria in your field, but as they continue on through the processing, we amplify what the potential issues are going to be. So through the picking process through the packing process and through further processing have additional areas. Where do you find Listeria? As we said we can find it in the environment because it is going to be associated with soil and water, so if you've got bins that are sitting on the ground and it's dirty and it's muddy, think about all of that Listeria that can come in on the bottom of the bins, and those are going to be a potential source of Listeria. As you're going to go through, and I'm not sure what your apple packing facilities look like, but the ones that I saw in Washington state, they ended up floating the apples out of the bins, so the dirty bins came down into the dump tank, and all of a sudden, you have dirt that's in your first initial wash, then as they go through, what I call this lazy river of mud, they are going to be inactivating any of the chlorine that may be there for your initial sanitation. Then, as you continue to process it, the Listeria is going to be picked up by the brushes, by the rollers, by the conveyors, and there's not a good kill step in that. 

So what are you going to be doing as a grower, as a packer? Are you going to be testing all your Listeria that's going to be coming in there? I can almost give you 100% guarantee you're going to find it there. So doing that detection of the apples as they're coming in probably is not going to be your best use of resources. On the other hand, what we need to do is once we understand that it potentially be contaminated how do we kill it, and that's going to be coming in with good processing practices and making sure we have good environmental controls. So with the environmental controls, I'd like to point out that United Fresh Produce Association has a document that's available for you to download, free of charge, all you have to do is sign up your information on that, but it provides some guidance as to how to do environmental controls. It's going to be complicated. If you don't have a good food safety background, it may not be necessarily something for you to be able to initiate all by yourself, but what we would recommend is that you enlist the help of an expert, of a consultant to be able to go through your system and find out where those harborage sites are, how you can set up your system to get rid of Listeria as best you possibly can, and how you're going to have a good environmental program. Number one is you're going to have to try to make sure that your whole processing area is going to be as clean and dry as you possibly can because Listeria doesn't like it when it's dry. Making sure that you have good sanitary design of the equipment of the facilities. If you have an old facility, it's going to be difficult, but if you're going to be doing any kind of remodeling, new building, this is going to be your opportunity to make sure it's done right. Things have to be cleanable. 

You have to be able to disinfect, heat sanitize is necessary. When we're looking for Listeria in the environment, we are going to be really look hard for it because once you can find it, then we have to fix it, and we want to be able to keep it out. So how do you test for Listeria? Once again, this is where you're going enlist the help of either a commercial laboratory or some other kind of consultant. Make sure that they help you identify what are going to be the troublesome areas. We typically are going to be looking for general Listeria species rather than specifically monocytogenes. We're going to have a combination of targeted areas as well as random areas to make sure that we know where the Listeria is, and then once again, once you find it, you're going to have very targeted massive cleaning and sanitation in there. Well what we can do also are simple hygiene checks, and if you haven't been familiar with ATP detection, basically it's a hygiene indicator, and if you come up with a positive on that, that means you have to clean and sanitize again. The sanitary zones that you're going to be concerned about, certainly are going to be the product contact surfaces, so those will be the slicers, conveyors, any utensils, people hand workers from the workers, but also are going to be the areas that are going to be adjacent to those areas are going to be problematic 'cause the Listeria can basically move around the food processing environment, but also things such as phones, lifts, other types of non-product contact surfaces and a little bit further away. So as I said, what we're going to be doing is we're going to try to make it clean and dry, then after it's clean, we're going to sanitize it, we're going to try to do that dry clean-up, and then a wet clean up, quaternary ammonium compounds and other peroxyacetic acid sanitizers seem to be most effective in that. For the apple itself, if you're going to be doing that dump tank, and you're going to be using chlorine initially, you have to make sure you have active chlorine in there because that dirt is going to take away, or inactivate, that chlorine. 

Then, once you get through that initial step, then taking a look at other options such as chlorine dioxide that you can put into the water, peroxyacetic acid, all of these have some efficacy, but they aren't going to be the magic bullet. They're going to have to be done in tandem with each other, and making sure you don't cross contaminate. So what can a packer do? Number one is be aware where you have potential contamination sites, minimize contact with domestic animals, keep the bins clean, reduce the contact with decaying apples because those can be really high levels of Listeria in there, modify the dump tanks so you prevent that cross contamination with the real dirty apples with ones that you think are going to be fairly clean, use multiple sanitation including spray bars, so you aren't letting it sit into that dirty water all the time, making sure that you clean the equipment, high pressure, steam might be good, making sure that you're going to be using maybe quaternary ammonium compounds on the brushes, and then certainly the environmental testing is going to be part of the picture. There are still a lot of knowledge gaps, and we don't know exactly how all the sanitizers are working if they're going to get us everything that we want to be able to do out of it. What are going to be some other niches? What are going to be something that we're going to be able to do to help reduce the number of Listeria that might be in an environment? And so there's still a lot of research that has to be done. We are really at our infancy to understand Listeria control in fresh produce items, but we are going to be able to work on this eventually. So, number one is we need to make sure the Listeria stays out of our packing environment to begin with, and the way we can do it is by controlling in the fields by themselves, making sure our bins are clean, making sure we don't have that cross contamination. Understand that listeriosis is going to be associated with foods that support growth. The surface of an undamaged apple is not going to be one of those, but once you do damage it, cut into it, bruise it, then it can potentially be an issue. We will anticipate that we're going to see more listeriosis outbreaks in the future. 

We have much better epidemiological tools for tracking and being able to put the pieces of the puzzle together, so we can find out that some of these things are not sporadic cases, but they're really associated with a particular food item, and one other thing is that we are engaging in additional research to help validate that our sanitation and our processes are really going to be working. So with that, I thank you very much for your attention, and if you do have any specific questions, I have my email address on that. It's kglass@wisc.edu, thank you. (applause)