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The Dose Transcript for January 9, 2025

Host: Dr. Brian Goldman

BRIAN GOLDMAN: I'm Dr. Brian Goldman. Welcome to the Dose. Winter is not just the season for colds and flus. Unfortunately for many of us, it is also a season for vomiting. And the cause is a bug called norovirus. It used to be called Norwalk virus because it was first described in an elementary school in Norwalk, Ohio. Norovirus is a common cause of illness outbreaks on cruise ships, [in] schools and daycares, and lots of other places where people congregate. Cases of norovirus are on the rise in the U.S. The Public Health Agency of Canada says cases here are spiking above the five-year average. Personally, I've had it at least three times and would rather not get it again. So this week we're asking: What should I know about norovirus? Hi, Zain. Welcome back to The Dose.

ZAIN CHAGLA: Hi, Brian. Thanks for having me.

BRIAN GOLDMAN: Have you ever had norovirus?

ZAIN CHAGLA: Yes, I did. Two-and-a-bit years ago. And it was memorable, to say the least.

BRIAN GOLDMAN: What was the most memorable part of it?

ZAIN CHAGLA: It came from my daughter who was in daycare at the time, which is, you know, a big area. And I think it was the seeing the dominos fall one by one, you know, in the family. And knowing it was coming it was almost that imminency that was the memorable part. And then one morning you wake up and it's like, it's my turn now, I guess. And how fast it hits and how good you recover from it right afterwards.

BRIAN GOLDMAN: The thing that sticks out in my mind is the suddenness. Going from feeling perfectly well to a few grumbles, a burp or two, and then rushing to the bathroom to throw up. I think people want to know how to detect it, what to do about it. So let's get into our conversation. But before we do, can you give us a hi, my name is? Tell us what you do and where you do it.

ZAIN CHAGLA: Hi, my name is Zain Chagla. I am an infectious disease physician. I teach at McMaster University where I'm an associate professor, and practice at St. Joseph's Healthcare in Hamilton.

BRIAN GOLDMAN: What do we know about why norovirus cases are on the rise right now?

ZAIN CHAGLA: So there is a seasonality to this disease. I mean, the moniker, one of the monikers for this disease is 'winter vomiting disease,' and well, it's winter, and people start vomiting. And so there is a seasonality. Again, probably multiple factors -- immunity, people getting together, close contact environments, more inside interactions. And in particular with close contact environments, where we see the virus spread quite a bit. And so, not unexpected. And in many, many years past, we see this uptick in November that really, really rushes up through the holidays and then starts kind of fading out in March and April. Although there is seasonal norovirus transmission that is not only limited to this winter season.

BRIAN GOLDMAN: What influence has the pandemic played on norovirus cases in North America?

ZAIN CHAGLA: So I think there's two things. One is, you know, with every kind of contagious disease which requires human contact, what happened during the pandemic has... you know, with limited human contact, closure of a lot of these settings, insane emphasis on environmental control, there was less transmission. But I think the other part of the pandemic, especially in the context of more resources for diagnostics and more emphasis on making appropriate diagnoses, the case ascertation [sic] rate in terms of us actually diagnosing norovirus cases that are coming to health care outside of, you know, certain settings which were monitored before, is also higher. So it is likely a combination of the two. We disrupted patterns. They're now back to normal. We do know norovirus has a very low, short immunity, and so, you know, people can get reinfected while they're going through their first post-pandemic infections now. And we are diagnosing more cases because of the emphasis on making diagnoses rather than making syndromic kind of diagnoses and management.

BRIAN GOLDMAN: Are there certain kinds of populations in which we're seeing increased case counts? There have been reports about cruise ship outbreaks. Where else?

ZAIN CHAGLA: Children-under-5 centres, daycare centres, preschools. That's the classic transmission pattern. The United States actually documents kind of outbreaks of norovirus. Some of the settings that, you know, we typically see, again, are institutions, hospitals, long-term care institutions, where we do that syndromic surveillance and actually have access to testing. Classically, we see these close contact settings. So cruise ships are one, barracks, other health-care institutions. Really, you know, where people live in that environment for a significant amount of time, and hygiene may not be as ideal as kind of a typical workplace setting.

BRIAN GOLDMAN: Any idea where in Canada cases are on the rise?

ZAIN CHAGLA: There was a recent email from the Public Health Agency of Canada just advising the increase in cases. We do have a national enteric gastrointestinal disease surveillance network that does do real-time monitoring of situations. The provinces that were called out were Alberta, British Columbia and Ontario. Although I would just be very cautious about long-term interpretation of the data. It has to do as well with what centres have access to, you know, PCR testing for norovirus. And so there may be activity in many other provinces, but certainly those three provinces were called out in terms of increasing activity.

BRIAN GOLDMAN: Let's dig deeper into how the virus spreads. What can you tell us about that?

ZAIN CHAGLA: This is a really unique virus in the context that it is very environmentally stable. The thing that prevents us from getting many viruses is that they can't live in the environment for a long time. It's, you know, exposure to different temperatures, it's exposure to cleaners, it's exposure just to open air that leads to viruses breaking down in the environment. Not to say we can't get an impact from the environment, but this virus is very, very unique in the context that it can actually maintain its stability through a range of temperatures, from freezing up to 60 degrees in some studies. It can stay on objects for a significant amount of time, up to weeks to months depending on the object and the moisture within that object. And it is more resistant to typical cleaners, like what we use in hand sanitizer, for example, than other viruses. And so the combination of these makes it very easy to get into the environment. And the amount that actually infects people, so actually makes them sick, the amount of virus you have to expose people to, even 15 viral particles. So, you know, you're talking about microlitres of virus that actually need to infect people. Very, very small infectious burden, stability in the environment, and, you know, this is spread by fecal-oral spread. Guess what? You know, when you have norovirus, things are coming out of both ends. And so that's highly infectious material coming out of both ends very quickly. Little needs to infect people and can stay in the environment for a long time. So it's really a combination of these factors that makes it really, really infectious in certain settings. Especially when hygiene is poor, people are close together and really kind of ripping through a household very quickly.

BRIAN GOLDMAN: So what you vomit could be infectious, what you poop could be infectious, and it only takes a small amount of it. So if there's any residual virus particles left on your hands and you touch somebody else's utensils or food or plates, there's a good chance that they're going to get infected too, if they consume anything using those utensils or the food that you may have contaminated or the plate that you may have touched.

ZAIN CHAGLA: Yeah, absolutely. And, you know, the biggest, you know, reservoir of this is kids. Guess what? Kids under five are not, A, not continent, a lot of them. B, you know, don't have the best hand hygiene. And when they're feeling terrible with vomiting and diarrhea, they're going to contaminate everything around them. So you can imagine how it would rip through a daycare quickly. You know, my case, where the kid came back to the household, it went through all of us in the household very quickly because, you know, parents take care of their sick kids. They're not going to be as focused on necessarily the hygiene, but just making sure their kids are doing all right and giving that love and attention that they need. And, you know, as you said, it can get on a lot of different things. It can get on food, it can get on plates, it can get on toys, it can get on multiple other things. You know, when we flush the toilet, for example, and the toilet seat's up, it can get into the environment around it. And so we see norovirus, not only as this winter vomiting disease which kind of spreads person to person because hygienic issues, but, you know, norovirus is a very common cause of travellers' associate diarrhea. You know, you can imagine in areas of the world, you know, food handlers could put it on food. That's typically the traveller, you know, travellers' diarrhea. We see this as outbreak-associated diarrhea in health-care settings. And again, you can imagine that patients that are not continent in a health-care system could spread it in the environment very quickly. And so, it is this unique virus that is not just this gastroenteritis or stomach flu that we see in the wintertime, but really is a virus that causes a lot of our diarrheal illnesses, in general, throughout multiple different settings.

BRIAN GOLDMAN: I had heard maybe a few years ago that it's possible, at least it's theoretically possible, for virus particles that briefly circulate in the air. You know, if you happen to walk into a bathroom with an obvious smell, an odour, indicating, you know, recent diarrhea that's been passed into a toilet, that you could actually inhale air particles and get sick. Is that true?

ZAIN CHAGLA: There was actually some data in SARS-1 where this happened in some of the apartment buildings in Hong Kong. And it had to do with the ventilation systems, and essentially air was being vented into apartments from other toileting areas. So again, should be vented out. It was actually vented the wrong way, and then led to spread kind of -- very great epidemiologic studies. We could actually see the spread along the ventilatory pathways of those connections. So absolutely, you know, and you can imagine just from a mechanistic standpoint. You know, you have your poop in the toilet, you flush the toilet, you see that splashing of the toilet. So, yes, the air itself can be contaminated. But you can certainly imagine the environment around the toilet as being contaminated because, you know, there are some water droplets that go into the environment when you flush the toilet. And so even with good continence in the toilet, being able to go in the toilet, doesn't mean that the toilet itself is going to be completely sterile, and flushing may actually introduce that into the environment.

BRIAN GOLDMAN: Obviously, this illness causes nausea and vomiting and it also causes diarrhea. What are some of the other symptoms, typical symptoms of norovirus?

ZAIN CHAGLA: People get a mild fever. It may or may not come. Obviously, the symptoms of dehydration can lead to muscle aches and headache. Some of it's related to the virus itself, but some of it is just related to the fact that you're dehydrated and malnourished for a couple of days. So that can be certainly part of it. And, you know, the major complication I think we see that leads people to health care. Most people do fine. They feel terrible for two days, but most feel fine. But I think we recognize that there are certain patient populations where that two days of dehydration can set off a significant cascade of illness. And so young children, people with comorbidities, older individuals, people with kidney disease, that dehydration for a significant amount of time can be compromising to them and may lead them to needing health care to deal with it.

BRIAN GOLDMAN: But in general, this is a self-limited illness. And I guess for some people it can persist.

ZAIN CHAGLA: There are some rare populations where their ability to clear the virus, which is usually very robust in most individuals, but the very, very immunocompromised, and we're talking organ transplants, stem cell transplants, very, very limited number of medications where their ability to clear the virus is much, much slower. I've done some work in this field. They often present with very prolonged kind of low-grade diarrhea associated with the illness. And again, usually can be mitigated by some medical interventions, but a little bit different than that, you know, explosive vomiting, explosive diarrhea and recovery over three days.

BRIAN GOLDMAN: Now we want to get into the important subject of prevention. How can people avoid norovirus?

ZAIN CHAGLA: Person-to-person contact, fecal-oral spread. So, handwashing. It's not perfect, but it's still good. So even just good soap and water, especially as we're going into these high contact environments. So, you know, a parent that's picking up their kid from daycare -- good idea to wash their hands before they pick up their kid, just because that environment's contaminated. Or when they get home after picking up that kid. If places are experiencing a norovirus outbreak, even a home, the people that are still well may want to focus on cleaning of the environment, cleaning of the toilet. Just recognizing that if they can mitigate that spread in certain environments, that they may not have one or two family members out, there may just be one, which is, you know, much better than not. Certainly there are certain settings which are super high-risk where you want to pay attention to environment, because there is likely someone with norovirus that's coming in that environment. I think the classic one we talk about is cruise ships. Being on a couple of cruises recently, there is a huge emphasis on hand hygiene at every point of entry. So when you're eating food, consuming beverages, coming in and out of certain environments like high-contact environments, that you wash your hands aggressively and, you know, carry that hand sanitizer around you at all times. Just recognizing that this year has actually been, from the CDC, one of the highest norovirus years on cruise ships for, you know, the reason that there's a lot spreading in the communities. And again, it's a contact setting. There are a couple of other unique populations for norovirus in terms of food consumption. Oysters are one food that is very implicated in norovirus outbreaks. And the reason being is oysters are kind of the filter of the sea. You can imagine if there's any contamination locally with human feces in that water, that, you know, oyster is essentially filtering it. We eat them raw, cold. Certainly has been seen in similar spot prawns, I think, were implicated a few years ago. You know, similar type argument. You know, raw seafood, especially seafood that was exposed to human waste in certain settings, can be a risk factor in that context. So people who are very worried may want to avoid those foods, or at least make sure they're cooked, recognizing that sometimes changes the flavour or taste profile of all of it.

BRIAN GOLDMAN: You mentioned handwashing and you mentioned hand sanitizer, and I think there's an important point that I want to underscore here. How effective are hand sanitizers in reducing the spread of the virus, say, compared to handwashing?

ZAIN CHAGLA: Some of the agents in hand sanitizers -- again, there's a spectrum -- have some reduced activity against noroviruses compared to other pathogens. And so, not to say it's zero effectiveness. It depends on burden, it depends on where on your hands. It depends on how you use hand sanitizer on your hands, so if you're getting every orifice versus getting just the base of the palms. Handwashing with soap and water is still -- and warm water -- is still a very effective intervention and still has very good capacity to kill norovirus on that. So, you know, if you have the option, you know, especially in the context of hands being soiled, and you know, taking care of kids with norovirus, you want to probably use soap and water first to make sure that everything is off your hands. If you have nothing, then hand sanitizer is better than nothing. But this is probably one of the opportunities where good old soap and warm water is still probably the better intervention going forward.

BRIAN GOLDMAN: As you've already said, norovirus can stay on surfaces like countertops, toilet handles and utensils, doorknobs. For those surfaces that are not for serving, like they aren't serving pieces or plates, how would you clean a countertop?

ZAIN CHAGLA: General day-to-day is different than someone who has norovirus in the household. There is some resistance to chlorine-based products. Bleach-based products are probably not unreasonable, recognizing that you want to know what you're doing when you're handling them in that sense. Soap water is still not an unreasonable intervention. Just making sure that you're being thorough, going through things. For those things that could be heated -- linens, undergarments, that type of thing -- a good wash is still very, very reasonable. You know, soap and water, long time heat and drying, like, still enough to kill in the environment. So it's simple things. It's not necessarily crazy. But, you know, for example, that toilet in your house, bleach-based cleaning, especially when someone's suffering with noro, if you're trying to prevent spread in the household, is probably better than just the typical household sanitizing products.

BRIAN GOLDMAN: There's no specific treatment for patients with norovirus. What hydration do you recommend?

ZAIN CHAGLA: Depending on populations, there's different requirements. You know, for adults, just, you know, typical water; you may want to use electrolyte-based replacement; soups. That type of thing. Just be cognizant that people have irritable stomachs during the time, so they may want to modify their diets. But nothing wrong with water or electrolyte-based replacement. Certain kids, especially if they're able to, Pedialyte may also be a nice hydration tool. In low-income settings, we often use oral rehydration therapy, which is a rice-based, starch-based rehydration tool. But it's not the product, it's just making sure that we're cognizant of it. We're recognizing the stomach is a bit sensitive during that time, so just being cognizant, especially parents, you know, with kids, that they're replacing hydration as they're going through it. And if, you know, people are not able to hydrate, they're getting lethargic, they're really, really not able to keep things down for a significant amount of time, kids are getting no tears and sunken eyes, that type of thing, that may be a trigger to seek health care at that point because I.V. hydration may be needed.

BRIAN GOLDMAN: What sorts of anti-nauseants would you recommend?

ZAIN CHAGLA: Gravol can sometimes certainly help with settling things down. Again, people do want to be cognizant in terms of some of the side effects, in terms of sedation. It's not the best anti-nauseant, but again, may be able to just get people through that first 24 hours of vomiting and be able to keep stuff down. Some people do recommend Imodium when things are going through with diarrhea. It is a bit tricky because, you know, there's a physiologic reason to expel stool in that sense during the diarrheal phase. It's your body trying to get rid of virus, so you want to make that decision carefully. But, you know, I think the bigger things, these are symptomatic drugs. They're not meant to reverse the disease process. And, you know, really, really focusing on hydration more than anything else, recognizing it will pass for the vast majority of individuals, and you're really just trying to make sure that you can recover quickly from the other end.

BRIAN GOLDMAN: When should people seek medical attention?

ZAIN CHAGLA: The big thing is dehydration, the inability to keep fluids down significantly for 24 to 48 hours. People that are becoming lethargic because of their dehydration, and this is, you know, the inability to even get out of bed, being quite dizzy or not keep anything at all down. Certain patients who're on medications that are critical. So for example, a person with diabetes that can't take any of their medications, their blood sugars are getting out of control, they probably do need to seek medical attention to help with stabilization. For parents of kids, again, you want to make sure that kids are able to tolerate hydration, that their kids are not getting lethargic. You probably see it more than I in terms of the signs of dehydration amongst young children -- sunken eyes, poor tearing, very, very significant irritability, where they may want to seek medical attention there. Those are generally the big things in the context. And, you know, certainly, if there are other features that don't fit with norovirus that are severe. So, ongoing severe fevers, significant abdominal distension, blood in the stools. Those things that are not classic for norovirus whatsoever that people should still be seeking attention and not just saying, this is a typical stomach bug that will go away.

BRIAN GOLDMAN: Finally, Zain, where are we in the development of a vaccine against norovirus?

ZAIN CHAGLA: You know, as compared to a COVID vaccine, we can actually do human challenge studies here. So that's really cool because then we can develop vaccines, we can challenge people with the virus after they get vaccinated, and then, you know, see if things improve. Gastrointestinal viruses are really mitigated by antibodies in our gut, which is a specific response that's a little bit different than other vaccines that we trigger people with. You know, we have a rotavirus, which is a separate viral infection that causes diarrhea in young children. We actually use an oral vaccine to trigger that response, and it does a pretty good temporary job of controlling rotavirus in young children. So there are a couple of vaccine candidates. Some oral. One mRNA candidate from Moderna. And most of the data going through phase one and two have shown that you can mitigate some disease. You definitely trigger that specific antibody in the gut appropriately. But, you know, the long-term discussion of whether or not these are long-lived, recognizing that the typical reinfection pattern is, you know, six months to two years -- it's not, you know, immediately after vaccine -- if these are long-lived, if these are protective for a larger population, is ongoing. And there are phase three trials ongoing now. So, you know, hopefully we do see benefits. And I think, you know, it's a horrible illness, but, you know, recovery mostly in this setting. But this, you know, is a huge, huge burden in low-income settings. You can imagine norovirus on the background of chronic malnutrition, food insecurity, limited access to health-care resources. There are many children that die from this virus that is actually quite benign in our setting. There is a big global need to develop a vaccine, not only just for the inconvenience of the norovirus infection, but literally saving lives amongst some of these children.

BRIAN GOLDMAN: That's an important point to end our discussion on. Zain, thank you so much for coming on The Dose to talk about norovirus.

ZAIN CHAGLA: No problem. All the best, Brian.

BRIAN GOLDMAN: Dr. Zain Chagla is an infectious diseases specialist at St Joseph's Healthcare and an associate professor at McMaster University in Hamilton, Ontario. Here's your dose of smart advice. Norovirus is a highly contagious virus that causes diarrhea and vomiting. It's a common cause of illness outbreaks on cruise ships, and also causes outbreaks in schools, daycare centres, and other places where people congregate. The Public Health Agency of Canada says reported cases have risen above previous averages. Some of the increase may be due to underreporting of cases of norovirus during the pandemic. The U.S. Centers for Disease Control says norovirus is the leading cause of foodborne illness in the U.S. The disease has gotten the nickname 'winter vomiting illness' because outbreaks tend to occur more frequently during the fall and winter months when people tend to congregate indoors more often. The vomiting often begins suddenly and can be quite violent. Other symptoms include diarrhea, abdominal pain, body aches, headache, and a fever. Norovirus is so infectious that you can get sick by ingesting just a few virus particles. The virus spreads through direct contact with an infected person and by consuming contaminated foods and beverages. Consuming oysters has been implicated in some outbreaks. You can also get norovirus by using contaminated plates and utensils and by touching contaminated surfaces like taps, countertops and toilet handles. Norovirus is more durable than respiratory viruses like flu and can live on surfaces for days and even weeks. Most people recover within one to two days. Those who are immunocompromised or who have chronic kidney and other illnesses may develop more long-term symptoms. Antibiotics are not effective against norovirus. The main priority of treatment is to take fluids to prevent dehydration. These include water, juice, soups, sports beverages and electrolyte sources such as Pedialyte. See your health-care provider or go to an ER if you cannot hold down any liquids for 24 hours or more. Consider seeking help sooner if you're immunocompromised or have other chronic health issues. Take steps to prevent the virus from spreading through your household. Those with vomiting and diarrhea should not prepare food or handle the plates and utensils of others. Alcohol-based hand sanitizers may not be as effective at stopping the spread of norovirus as they are at controlling the spread of respiratory viruses. Washing hands frequently with soap and water works better. Wash hands before eating and after using the bathroom, and any time you touch a surface that may be contaminated. These include doorknobs, serving pieces and countertops. Currently, there are no licensed vaccines for norovirus. Several candidate vaccines are under development. If you have topics you'd like discussed or questions answered, our email address is thedose@cbc.ca. If you liked this episode, please give us a rating and review wherever you get your podcasts. This edition of The Dose was produced by Sameer Chhabra. Our senior producer is Colleen Ross. The Dose wants you to be better informed about your health. If you're looking for medical advice, see your health-care provider. I'm Dr. Brian Goldman. Until your next dose.

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What do I need to know about norovirus? - Transcript

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