Public Health

Norovirus outbreak: Is there a stomach bug going around? Norovirus symptoms and incubation period

. 11 MIN READ

AMA Update covers a range of health care topics affecting the lives of physicians, residents, medical students and patients. From private practice and health system leaders to scientists and public health officials, hear from the experts in medicine on COVID-19, medical education, advocacy issues, burnout, vaccines and more.

How long does Norovirus last? How to treat a stomach virus, current measles outbreak in Florida, a new study on long COVID symptoms and causes of brain fog.

Our guest is AMA Vice President of Science, Medicine and Public Health Andrea Garcia, JD, MPH, AMA Chief Experience Officer Todd Unger hosts.

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  • Andrea Garcia, JD, MPH, vice president, science, medicine & public health, American Medical Association

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Unger: Hello and welcome to the AMA Update video and podcast. Today we have our weekly look at the headlines with the AMA's Vice President of Science, Medicine and Public Health, Andrea Garcia. I'm Todd Unger, AMA's Chief Experience Officer. Welcome back, Andrea.

Garcia: Thanks, Todd. Appreciate the opportunity to be here.

Unger: Well, we have a lot to talk about this week. First up, seeing news about a, quote, "stomach bug" hitting the Northeast. Tell us more about what's happening.

Garcia: Yeah. So the virus is known as norovirus, commonly referred to as stomach flu, but it's not related in any way to influenza. And we've really been seeing cases across the country. As you said, in recent weeks, the hardest-hit region has been the Northeast. They're experiencing their highest rate of the virus since last April.

And if we look at the CDC data published last week, cases of norovirus have increased in New York City and across other states in the Northeast in recent months. That three-week average for test positivity for norovirus in the Northeast is at 13.9%. So that rate in the Northeast has remained above 10% really since the middle of December.

And to put that into some context, in the Western region, they're at about 12% positivity, the Midwest around 10% and the South is at approximately 9.5%.

Unger: Andrea, are those levels common for this time of year?

Garcia: So norovirus is somewhat seasonal. Those cases do occur most frequently in colder months so late fall, winter and then early spring. Nationally, norovirus positivity rates have really been hovering around 10% to 12.5% since early January.

And I think while that feels high, these levels are below where we were last season, when about 15% of tests were positive both nationally and in the Northeast. And according to the CDC, there are typically between 19 and 21 million norovirus infections in the U.S. every year. Most of them happen between November and April. And then we typically see about 109,000 hospitalizations and 900 deaths from norovirus each year in the U.S.

Unger: Andrea, it sounds like some of the cases can get pretty serious. And I know that it's extremely contagious. So let's talk a little bit about symptoms. What do people need to watch for? And how does it spread? And how do you keep it from spreading?

Garcia: So you can usually tell if you've been infected with norovirus pretty quickly. That symptom onset is typically pretty sudden. It can include nausea, stomach pain, diarrhea, vomiting, as well as fever headache and body aches.

As you mentioned, the virus is extremely contagious. It spreads easily through direct contact with a person who's infected as well as on surfaces or objects contaminated with the virus. It just takes a few particles to make someone sick. And people with the illness shed billions of virus particles both in their stool and in vomit.

So the virus we know can linger on objects and surfaces for days or even weeks. And it typically spreads pretty easily in crowded environments. So think like nursing homes, daycare centers, cruise ships. It's also important to note that, according to the CDC, an infected person can transmit norovirus even after they're feeling better for potentially up to two weeks. That best way to prevent norovirus is frequent washing and cleaning and disinfecting surfaces.

Unger: Well, I'll be washing my hands and not touching anything until this particular outbreak is over. Andrea, what about food, is norovirus the kind of thing that can spread through contaminated food?

Garcia: It is. And that's why it's sometimes referred to as food poisoning. So norovirus is a leading cause of foodborne illness in the country. The source is often contaminated water. For example, food can get tainted if like fruits and vegetables are watered with contaminated water. Oysters are another common culprit. They pose a norovirus threat if they're harvested from contaminated water.

We recently did see the FDA advise restaurants, retailers and consumers to avoid selling or eating oysters from Baja California and Sonora, Mexico, because they may be contaminated with norovirus. And you might recall that just this past December, there was a norovirus outbreak linked to a North Carolina sushi restaurant that sickened at least 241 people.

People can definitely help prevent foodborne norovirus by rinsing their fruits and vegetables with clean running water and cooking shellfish thoroughly. There is no treatment for the virus, but CDC recommends drinking lots of fluids. That's to help prevent dehydration. And on the bright side, the illness does typically pass for most people within a few days.

Unger: All right. Well, speaking of contagious, another illness that we have been talking about over the last several weeks continues to make headlines. That's the measles. Andrea, what's new this week?

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Garcia: So Florida has really been in the spotlight this week. And that is both because they're battling a growing measles outbreak, but also because the guidance the state surgeon general there has provided to parents and guardians on the outbreak. So that outbreak began a week ago when the Broward County School District reported six confirmed cases of measles at an elementary school.

In a letter last Tuesday, the Florida surgeon general noted that it's normally recommended that individuals, without a prior infection or vaccination, stay home for up to 21 days. That letter noted that the Department of Health there is going to defer to parents and guardians to make decisions about school attendance.

So we've seen the president of the AAP note that this runs counter to everything they've heard and everything they've read. It certainly counter to AAP policy. We've seen the chief medical officer for the Association of State and Territorial Health Officials put out a statement stressing the importance of adhering to established public health practices for measles and vaccinating the unvaccinated.

Measles is so contagious. It has such a long incubation period that not following those established public health recommendations can allow cases to spread. The CDC has said that unvaccinated people have a 90% chance of being becoming infected if they're exposed to the virus. And this is certainly complicated by the fact that a person with measles can spread the virus, starting four days before their rash appears, so before they even recognize that they have the disease.

Unger: Wow, Andrea, so that note from the surgeon general, obviously, creating quite a stir. Has there been any fallout since he issued that note?

Garcia: Well, we're now up to 10 cases of measles in Florida, nine in Broward County, one in Polk County. Two of these cases are reportedly in children under the age of four. And while the surgeon general's letter did not mention the importance of getting vaccinated, we do know that Broward County's local health department has reportedly been offering measles vaccine at the elementary school since the outbreak began. As a reminder, that vaccine has been shown to be 97% effective in preventing infection.

There was a Kaiser Family Foundation news article that pointed out that considering the dangers of the disease. The vaccine is incredibly safe. A person is about four times as likely to die from being struck by lightning during their lifetime in the U.S. than having a potentially life-threatening allergic reaction to the MMR vaccine.

Unger: So we have a virus that's highly contagious. We have a vaccine that is highly effective. Now one thing we haven't talked about is the, quote, "danger" of the disease itself. How serious can measles be?

Garcia: So measles can be serious. And we know it can lead to long-term complications. If we look at CDC's information, an estimated one in five unvaccinated people in the U.S. who gets measles is hospitalized. Ear infections occur in about one of every 10 children with measles and can result in permanent hearing loss. One to three out of a thousand children with measles will die from respiratory and neurological complications. And in rare cases, we know that serious can conditions can emerge even years later.

The most recent CDC data indicates that there are at least 35 measles cases in 15 states reported so far this year. In January, we saw nine measles cases in Pennsylvania, eight of them in Philadelphia. If there are no more cases reported there, this week, that Philadelphia outbreak will be declared over. Last Friday, we saw both Michigan and Indiana report their first measles cases in their jurisdictions since 2019. And it's been reported that Indiana case visited three hospitals here in Chicago while they were still contagious.

Dr. Paul Offit, I think, recently made a point that vaccines have been so successful that few people remember what it was like to live with measles. And he added, don't mess around with this disease it's not a disease that you want to relive. These cases really need to be taken seriously. We have a safe and effective vaccine for this disease and well-established public health guidance to help prevent the spread.

Unger: So great advice from Dr. Offit, a friend of the AMA Update. And we'll look forward to speaking with him soon as well.

Andrea, let's switch gears and talk about something that we haven't discussed much lately, and that is long COVID. There have been some new developments on the long COVID front. Can you tell us more about the details?

Garcia: Yeah. So we have a little more clarity about what may be causing one of the more frustrating symptoms of long COVID, and that is brain fog. We know that nearly 50% of patients who experience long COVID have reported brain fog. And earlier this week, an Irish research team reported their findings in nature neuroscience.

So those findings suggest that disruptions in the blood brain barrier along with hyperactive immune system are the likely mechanisms behind brain fog. This is not a new theory. But to test it, the researchers analyzed blood samples to look for any biomarker differences between those who did and did not report brain fog. They found that those who reported brain fog had higher levels of a protein that was produced by brain cells not normally found in the blood, which hinted a leaky blood brain barrier.

For the second part of the study, the researchers conducted brain scans using dynamic contrast enhanced MRI to examine brain circulation. And they found that long COVID patients with brain fog had a leaky blood brain barrier when compared to both long COVID patients and then to others who had recovered. They also found that long COVID patients with brain fog had increased levels of clotting markers in their blood.

Unger: So important finding. Andrea, what does it all mean?

Garcia: Well, it's important to understand those underlying causes of these conditions, so they can inform the development of targeted therapies for patients in the future. And I think it's important to note that this isn't true just for COVID. As one article states, the concept that many other viral infections lead to these post-viral syndromes might drive blood vessel leakage in the brain. And it's potentially game-changing.

These findings could change the understanding and treatment of post-viral neurologic conditions. And the findings also confirm that neurological symptoms of long COVID are measurable with real and demonstrable metabolic and vascular changes in the brain, which is huge. And I think it also importantly serves as validation for all those who've been suffering from these symptoms of long COVID.

Unger: Absolutely. That's a really fascinating study. And we're going to continue to watch as that evolves. That wraps up today's episode. Andrea, thank you again as usual for your perspective and being here to keep us informed.

If you found this discussion valuable, you can support more programming like it by becoming an AMA member at ama-assn.org/join. We'll be back soon with another AMA Update. In the meantime, you can find all our videos and podcasts at ama-assn.org/podcasts. Thanks for joining us today. Please take care.


Disclaimer: The viewpoints expressed in this video are those of the participants and/or do not necessarily reflect the views and policies of the AMA.

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