Season 6 | Episode 5

 

 

Joe McIntyre (Host): Welcome to another episode of the Merck Manuals Medical Myths Podcast. On this show, we set the record straight on today's most talked about medical topics and questions.

Listeria and foodborne illness have been prominent topics in the news lately, but what exactly are they and where do these risks come from? In this episode, we will define what a foodborne illness is and take a closer look at Listeria and listeriosis while sharing best practices for keeping you and your family safe.

I'm your host, Joe McIntyre. Our guest today is Doctor Larry M. Bush, an infectious disease specialist. Dr. Bush is an affiliate professor of medicine at Charles E. Schmidt College of Medicine at Florida Atlantic University and an affiliate associate professor of medicine at the University of Miami Miller School of Medicine.

He wrote a chapter on listeriosis that can be found on the Merck Manuals website. The link to that can be found in the episode description. Doctor Bush, thank you for joining us.

Dr. Larry M. Bush: Thank you for having me.

Host: Let's first start off with educating our listeners about foodborne illness generally. Can you explain what that is?

Dr. Larry M. Bush: A foodborne illness or a disease resulting from the ingestion of a wide variety of foods that have either been contaminated by a pathogenic micro-organism, most commonly by a bacteria. It can be a parasite or a virus or bio-microbial toxin, which is a toxin that an organism produces either prior to eating it or after you've eaten it, and even by chemicals.

Host: Now, what is the difference between a foodborne illness and a stomach bug?

Dr. Larry M. Bush: A stomach bug is sort of a lay term. A stomach bug, in essence, is the only organism that we really know that infects the stomach is Helicobacter pylori, or H. pylori, which is commonly seen in people who have ulcer disease and occasionally can cause cancer in the stomach. It's really not the stomach that gets infected, but it's the small intestine, and we call that enteritis, or the large intestine, and we call that colitis. Often, when people say I have a stomach bug, what they're referring to is a brief diarrhea disease, most commonly secondary to some of the viruses that we encounter all the time.

Host: What are some of the most common sources of foodborne illness in the United States?

Dr. Larry M. Bush: Well, it depends on the organism, but the majority of them either come from beef or pork or poultry. Additionally, fish, particularly shellfish and contaminated water. Some of these things come from sprouts or melons or plants that we eat. There's a whole range, but I think most people think of them with contaminated beef or pork, poultry, shellfish, other types of fish, and delicatessen meats. We know that Listeria is associated with various cheeses and unpasteurized milk.

Host: What are the other specific foods or handling practices that people often overlook which could pose or create some risk for foodborne illness?

Dr. Larry M. Bush: I think the major thing is undercooking and thinking things that can stay good in the refrigerator for a longer period than they're really meant to be, as well as keeping things outside the refrigerator. It's probably a common practice for people to defrost food outside of the refrigerator and within a few hours the surface becomes defrosted, and even though the center may still be icy, the surface can have organisms contaminated.

Other ones are not washing off your things, your plants and vegetables. Not washing any utensils and the devices that you're using to cut or store these things, putting them next to each other in the refrigerator.

One common thing that goes unnoticed is raw chicken. People tend to wash raw chicken off in the sink before they use it. That can contaminate other things that are in their sink or other food products that are nearby. If you're going to fry, for instance, chicken breast, it goes directly into the pan and should not be washed off. Those are common issues that increase our risk of developing a foodborne illness.

Host: Does cooking food thoroughly kill all types of harmful bacteria? And to follow up what does cooking thoroughly even mean?

Dr. Larry M. Bush: Well, the CDC publishes documented data on how much the temperature has to reach for certain types of meat. For instance, for beef, veal, goat, and lamb, the recommendation is 145°, and the only way you would know that is not by the
temperature we set on our ovens, but by using a thermometer and I know most people probably do not do that. For chicken and turkey, it's recommended that these be 165°.

For eggs, it's also 160° or cooking until the yolk and whites are firm. Ham has a lower temperature of 145°, and for leftovers, they should be reheated to 165°. It's variable depending on what type of food you're using, and again, it's really based on using a thermometer and not going by the temperature that's on the oven that we use because it's the inside of the product we're cooking that really counts the temperature measurement and not the outside.

Host: What is the reason that certain meats each have different temperatures to be cooked thoroughly? Why is poultry different from beef?

Dr. Larry M. Bush: First, the type of microorganisms present in the food matters, as each is sensitive to specific temperatures. Proper cooking is needed to eliminate bacteria. Second, the thickness and density of the meat play a big role. If the meat is very thick, tightly packed, or uneven, the heat may not reach the center properly, leaving parts undercooked and potentially unsafe to eat.

Host: You also mentioned the safe temperature to cook eggs, and I'm sure some of us, myself included, have had a few cocktails with potentially raw eggs in it, or egg whites in them. Is that safe? Is there a significant danger to drinking those types of cocktails or consuming eggs that have not been fully set, either the whites or the yolks?

Dr. Larry M. Bush: Yes, although it's uncommon those may be contaminated with certain bacteria that are prone to be found in poultry or chickens. When you think about the vast majority of people who contract a foodborne illness, either asymptomatic, never get diagnosed or were fortunate in the food or stuff that they're eating just does not carry the bacteria or a sufficient quantity of the bacteria for many of these organisms. It's not just that the bacteria is present. It's also the quantity that has to be present to produce an illness that's symptomatic.

I'm not sure I said this at the beginning, but it's felt that there are about 48 million cases of foodborne disease in the United States every year, and that's hard to know because as you would expect, most people don't go and get examined or tested. Therefore, it's not reported it's a transient gastrointestinal symptomatic disease, but out of those 48 million, about 125,000 get hospitalized and about 3,000 deaths related to foodborne illnesses every year in this country.

Host: Is food poisoning always noticeable immediately after eating contaminated food? Basically, does it require a stomachache or diarrhea or some other symptom for you to know the food poisoning, or can you have it and not even know it?

Dr. Larry M. Bush: Most people probably have it and don't even know it, and they may have some indigestion or transient cyanosis or slight diarrhea. It also depends on which organism you ingest. As I said, the ones that form toxin outside the body and what you're actually eating is the toxin that's been placed in the food where the organism is living. That's very typical of Staphylococcus, as it produces several types of toxins. One of them may be produced in the mayonnaise or the salad that you're eating and the toxins present. In those particular instances, the person gets ill rather quickly, and the illness is a transient nauseous vomiting that may come on even six hours later and go away within 12 hours. That's the same thing we hear about reheated rice, where an organism called Bacillus cereus can live and that also can produce a toxin outside of the body and produce a quick onset of nausea and vomiting.

Other organisms have to percolate, so to speak, in our intestine. They invade the intestine, then they inflame the intestine, and that could take one to three days. Then they'll present with more systemic illnesses like fever, abdominal pain, severe diarrhea. And then Listeria. We'll talk about that some more. Listeria can invade the intestine and invade other organs that may not become evident until days and weeks later. That's why Listeria is so severe. The concern in pregnant women because they may be asymptomatic for quite some time. It does damage to the child, as they can be born with Listeria and it's a common cause of premature labor and stillbirth.

Host: How can someone avoid Listeria? For instance, if a mother doesn’t know she has it—or may not find out for weeks or even until birth—what steps can be taken to prevent it? Is it as simple as following dietary guidelines, or are there other ways to detect or educate yourself about having Listeria?

Dr Larry M. Bush: There are strict guidelines that I'm not sure if many obstetricians actually discuss or present to their pregnant patients about foods to avoid, and what you're really looking for are diseases that would be more severe in pregnant women. Pregnancy is an immunologic deficient state and the reason for that is because the woman is carrying another being almost like a transplant, and you don't want your immune system to attack it. When we think of some of these diseases, they're more severe in people at the extremes of age, very young or very old. Both extremes have either underdeveloped immune systems or immune systems that have waned. They are severe in people who are taking medications that are known to lower their immune system. We see a lot of these advertised on TV for diseases like psoriasis, Crohn's disease, inflammatory bowel disease, rheumatoid arthritis.

Obviously, people who are receiving medications because of transplants or even people with diseases that are common day now, such as HIV or AIDS, and those particular persons have to be very cognizant of what they're eating. For the normal person, eating Listeria bacteria may cause no symptoms, and pregnant women have a 10 to 17 to 27 times higher risk of having a severe disease. The interesting thing about Listeria is since the symptoms may come on so many days after exposure, it's very hard to do contact tracing to figure out who was around the same type of food at the same time because they present at different times.

Host: Is this a reason why pregnant women are often it's recommended to avoid lunch meats and sandwiches that have deli meats in them?

Dr Larry M. Bush: Absolutely, soft cheeses, certain fruits, certain melons, certain types of shellfish and other types of fish. Pregnant women may think that keeping the food in the refrigerator keeps it well, but Listeria likes to grow in cooler temperatures, so there's a whole list of foods that pregnant women are particularly warned against. I'm not sure how often that information is provided to them by their obstetrician, but certainly they could ask.

Host: We often hear about the sniff test where if you smell something and it doesn't seem right, that means it probably isn't. Even if a certain food passes the sniff test. Can food that looks and smells fine still be contaminated?

Dr Larry M. Bush: Well, unless the quote sniff test has something to do with the odor of the food that's normally there. When we think of why somebody has bad breath or why their bowel movements may have a particular odor, sometimes people complain of odor in their urine. It's really the byproducts of bacteria or the bacteria themselves dying that produce odor; that's what gives us bad breath.

So if you have a quote “sniff test” and the food smells like it should not. The assumption would be that there is bacteria. It's heavily laden with bacteria that are produced by products or that are dying and not dying, and by-product production produces that odor. I would certainly avoid them. Not only dispose of it but clean the surface that they were on. If you stored them in a refrigerator, you need to make sure that you clean everything in that refrigerator. If you have food that's been sitting up against them, that should be discarded. It's important when you put food such as poultry and beef in the refrigerator. You separate it if it's open and not in the container for many of your other foods.

Host: You mentioned a few issues where you wish more doctors spoke to their patients about potential issues, especially for pregnant women. As an infectious disease specialist, are there any other tips that you would recommend that we haven't talked about so far for people to avoid eating certain foods based on their population, their gender, their whether they're pregnant or not? Are there any other recommendations that you have that we haven't talked about so far?

Dr Larry M. Bush: The immunocompromised people that we talked about and a lot of people think, well, my immune system's fine, but if you're taking even a high dose of Prednisone, a common corticosteroid medication for various reasons. Once you've been on it for several weeks and we're only talking around 3 weeks, your immune system does become defective to some degree, and we don't necessarily measure that to say, well, how much is my immune system down? So I would recommend all those people. Be careful with some of these foods, undercooked food, food lying out, foods that are known to carry certain bacteria that you would not know because of the taste. Additionally, deli meats, shellfish, etcetera.

I don't know if you've ever noticed or your listeners have noticed that if you go into seafood restaurants, it tells you that if you have underlying immunosuppressive disorders or you have liver disease that should really avoid shellfish because shellfish can carry something called Vibrio vulnificus. People who have underlying diseases may have a really severe, complicated infection. Not just gastrointestinal, but infections that will cause what we call necrotizing fasciitis, which destroys the soft tissues on your arms and your legs. So those types of folks clearly have to be aware of what their immune system may or may not tolerate. And even though we like to dwell on eating certain foods, I would clearly avoid them.

Host: Are there any other myths that you find yourself busting or coming across, whether it's friends or colleagues or potential patients or those students you come across asking you these questions that you often find yourself busting often?

Dr. Larry M. Bush: I'll tell you one myth that's very interesting. People think if they eat in a so-called 5-star restaurant, the chance of getting ill from the food is very small. All foods are checked by the FDA and they go under their practices. But five-star restaurants, if you walk into the kitchen of a 5-star restaurant as opposed to, let's say, a fast-food restaurant like McDonald's or Burger King. The people preparing the food in a five-star restaurant, and you may notice this on these chef shows on TV, well they don't wear gloves. If they happen to be transmitting any organism asymptomatically in their stool, it's likely to get on our food. So, the highest rate of food illnesses, if they're related to a restaurant, usually are in high-end restaurants, so to speak.

Host: As we wrap it up here, I know we talked about a handful of foodborne illnesses. Can you tell us what is the most common? What is the most common that you come across? What is the one that you see most often here in the US?

Dr. Larry M. Bush: I don't come across it that much and partly because it's self-limited for most of the time. People tend to get better after an acute illness which would either be nauseousness, cramping or diarrhea. They don't get very ill; it doesn't spread to other parts of the body, so therefore, you don't get somebody with a gastrointestinal foodborne disease and now winds up with a brain or a spinal fluid infection like that could happen with Listeria. The other thing is it's very contagious and the answer is norovirus. Norovirus is the number one foodborne illness in United States. We always associate it with cruise ships and the reason for that is because it's so contagious and people are so contained and going to the same dining room over and over and over that a lot of people get ill.

Norovirus is transmitted in seafood is transmitted in salads. Therefore, you get to really wash off your lettuce when you're preparing your salad, etcetera. But that is the most common illness in the United States that people don't give much thought to. Because they say, “Well, I haven't been on a cruise.” You don't have to be on a cruise. The difference on a cruise is its very close contact with the other people on the ship with you.

Host: Are there any tips that you have to avoid it other than not going on a cruise?

Dr. Larry M. Bush: Well, one, it's who is preparing the food, so you don't have a lot of choice. But two is to carry hand sanitizer with you and use it, not sparingly, but use it quite a bit everywhere you go. It will eliminate the norovirus on your hand before you get it into your mouth.

Host: Well, Doctor Bush, thank you so much for joining us on the Merck Manuals Medical Myths podcast. If our listeners are looking for more information about listeriosis or maybe other foodborne illnesses, where should they go?

Dr. Larry M. Bush: The CDC website is always a good resource for information that deals with diseases, et cetera. This is both treatment diagnosis and prevention. I would recommend the Merck Manual. I'm not just saying that because I'm involved in writing some of the chapters in the Merck Manual, I'm saying that because I can tell you, I teach medical residents and training and intern. Medicine and every one of them has it on their phone and their computer desktop because it's a great resource. I know how often it's up to date and I know the people who are involved in writing it. It's the most used medical book, both professional and consumer in the world.

Medical knowledge is essential; it has changed the world, and it will continue to do so. It is up to us to acquire that knowledge.

Host: Well, thanks again, Doctor Bush. I will let you leave our listeners here with the final word.

Dr. Larry M. Bush: Medical knowledge is power, please pass it on to your friends and family.