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Norovirus cases have been rising this winter in the U.S. RgStudio/Getty Images
  • Cases of norovirus, a highly transmissible “stomach flu,” are on the rise in the US, especially in the North East, according to the CDC.
  • The virus spreads more frequently during the winter months, causing severe vomiting and diarrhea.
  • Typically symptoms only last a few days and do not pose a serious concern for otherwise healthy individuals.

Cases of norovirus, a highly transmissible virus responsible for severe “stomach flu,” are on the rise nationally.

Data released by the U.S. Centers for Disease Control and Prevention (CDC) this month showed cases of norovirus rising throughout the U.S., especially in the Northeastern United States and in western states.

“Norovirus clearly is an extraordinarily transmissible virus. It’s said that it takes only about 10 viral particles, if you get them in your system, to initiate an infection. That’s really a very small dose,” Dr. William Schaffner, a professor of infectious diseases at the Vanderbilt University Medical Center, told Healthline.

Nationally, the number of positive norovirus cases is just over 12% but appears to be trending upward, according to the latest surveillance data from the CDC.

Last year, norovirus peaked in early March, which could indicate that there’s a final wave coming before rapidly tapering off into the spring, based on historical data.

However, the national trends don’t tell the whole story. Norovirus is appearing more frequently in the Northeastern and western United States.

In the Northeast, positive norovirus cases are 13% above the national average and have been for several weeks.

The next hardest-hit region is the western states, where cases are tracking similarly to the national average at around 12%. Both southern and midwest states are currently below the national average with 9% and 10% positive cases, respectively.

It’s unclear what is causing these regional variations.

Despite the current upward trend, overall cases of norovirus are not as widespread both nationally and regionally as they were in 2023.

This time last year, positive norovirus cases were at more than 14% nationally and 14-15% in the Northeast.

Like the flu, norovirus, which is also known by another colorful name, “winter vomiting disease,” tends to ebb and flow with the seasons and, as its nickname suggests, is most prevalent in the winter months.

“The seasonality of illnesses, whether they’re respiratory viruses or, in this case, norovirus, which is basically an enteric virus, is not really well understood, but it is well described,” said Schaffner.

Winter is prime time for the spread of viruses, which among other reasons, is often attributed to more people gathering indoors together, which makes transmission easier.

“Norovirus circulates all year round, but many times we do see an uptick in the fall and first couple of months of the year while people are indoors,” said Dr. Judith O’Donnell, Section Chief of Infectious Diseases at Penn Presbyterian Medical Center and a Professor of Infectious Diseases at the University of Pennsylvania.

Norovirus is already an extremely transmissible virus, but combining it with situations in which people are frequently in close quarters, like in the winter, can significantly increase the risk.

Places where norovirus tends to spread most often are environments like schools, healthcare facilities, and cruise ships.

If someone in your home contracts the virus, there’s a high likelihood that someone else can get it as well.

“As meticulous as you are, you’re going to have to help deal with that sick person,” said Schaffner. “It’s very difficult to avoid infection because this agent is so highly infectious.”

Stomach bug, stomach flu, or viral gastroenteritis — no matter what you call it, the symptoms of norovirus are bad news.

Acute or viral gastroenteritis refers to the inflammation of the stomach or intestines.

“Norovirus makes you quite ill. You feel quite ill for two, maybe into three days. You feel as though you’re going to die,” said Schaffner, who clarified that most people recover within a few days.

The hallmark symptoms of norovirus include:

  • diarrhea
  • vomiting
  • nausea
  • stomach pain

Less common symptoms also include:

  • fever
  • headache
  • body aches

Symptoms typically occur between 12-48 hours after being exposed. Although the symptoms tend to clear in just three days, they could be an excruciating few days.

Healthy individuals don’t have much to worry about in terms of serious symptoms from norovirus, but it is more dangerous for certain populations, including the elderly and small children.

The most dangerous effect of norovirus is dehydration caused by vomiting and diarrhea.

Since there is no antiviral cure for norovirus, the best treatment is supportive care, especially drinking lots of fluids.

“It’s the dehydration from the vomiting and the diarrhea that can give you a hard time,” said Schaffner. “The most important part of that is fluid repletion. Try to take fluids in, often in small amounts, but steadily to try to replete your fluid balance,” he said.

With norovirus, a little goes a long way, meaning it doesn’t take much to get you sick. When someone has a norovirus infection, they may shed billions of viral particles.

Norovirus commonly spreads through contaminated particles, such as feces or vomit.

The virus also spreads easily via a number of important pathways, including the following.

  • Food: Food can be contaminated by norovirus at any number of stages, from when it is harvested or prepared to when you put it into your mouth. If contamination occurs anywhere along this journey, it is possible for it to spread.
  • Water: Contaminated water is another way norovirus spreads. Water contamination can occur when sewage or septic systems leak into a clean water source. A sick individual can also contaminate water if they come into contact with it.
  • Surfaces: Like other viruses, norovirus can spread through surfaces. Contamination can occur from direct contact with a sick individual or spread from indirect particulate matter, such as when a sick individual vomits near a surface.

Due to the risk of contamination and spread through multiple avenues, the best prevention for norovirus is good hygiene. This includes common sense things like hand washing and regularly disinfecting surfaces.

“Frequent hand washing is the most important thing that you can do to try to prevent yourself from getting norovirus, and certainly always washing your hands after you use the bathroom and always washing your hands before you eat or drink,” said O’Donnell.

When preparing food, always wash fruits and vegetables. It’s also important to cook meat, poultry, and fish (including shellfish) to the correct temperature to ensure that any potential contamination has been neutralized.

Even if someone starts to feel better, norovirus can still be present in bodily fluids, so washing your hands and sanitizing surfaces are important both before and after symptoms are present.

Norovirus, sometimes known as the “stomach flu,” is spreading in the United States, especially in the Northeast, based on trends from the CDC.

The high-transmissible virus can cause severe diarrhea, vomiting, and nausea.

Symptoms typically pass within a few days. Since there is no cure for norovirus, prevention is key.

Good hygiene practices like frequently washing your hands and sanitizing surfaces are important prevention practices.