Norovirus illustration; This is not an example of the new strain, but the norovirus in general. (Credit: Kateryna Kon/Shutterstock)NewsletterSign up for our email newsletter for the latest science newsEvery winter, public health departments report a rise in illnesses. Most of these infections are expected during the colder months, and the data features the usual lineup of suspects acute bronchitis, influenza, pneumonia, and respiratory syncytial virus (RSV).This year has also seen a surge in norovirus, a highly contagious stomach bug. Starting November 2024, the percentage of positive tests for norovirus began to increase, which is to be expected in the colder months when people begin to congregate inside more.But by January 2025, almost one-quarter of the tests were positive, nearly double the rate of last seasons outbreak, according to the Centers for Disease Control and Prevention (CDC).Although the stats may seem scary, scientists know why norovirus infections are soaring this year. And they have advice on how people can protect themselves.Symptoms of NorovirusNorovirus, also known as the stomach flu, is a virus that hits the stomach and intestines, causing irritation and inflammation. Symptoms typically come on quickly and often violently. People experience diarrhea, nausea, stomach cramps, and vomiting.Norovirus might seem similar to food poisoning, and both are common illnesses, but the pathogens are distinct. In a typical year, as many as 1 in 15 people in the U.S. will contract norovirus. Most people recover on their own within a few days, but about 109,000 will require hospitalization, and 900 will die.Norovirus is a common virus that is the main cause of gastroenteritis in the U.S., causing about 60 percent of all cases the majority of 'stomach bugs' that people develop, says Robert H. Hopkins, Jr., a physician and the medical director of the National Foundation for Infectious Diseases (NFID).How Does It Spread?Norovirus spreads easily in places where people congregate, like schools, nursing homes, and restaurants. Cruise ships have also been susceptible to norovirus, and outbreaks are tracked by the CDC. Already, two ships in January 2025 were identified as having norovirus.Norovirus is a hardy bug, which makes it easier to spread between people. Norovirus is stable on surfaces for many hours and is not affected by the use of hand sanitizers or mild household cleaners.It also easily passes from person to person through contaminated food or water or when people share utensils, Hopkins says.The reason hand sanitizer cant kill the bug is because the virus does not have an outer coating. Norovirus is covered by a protein capsid that is only disrupted with soap and water or bleach solutions, Hopkins says.And this year, new strains of norovirus are introducing people to a bug in which they lack immunity.A Surge in Norovirus for 2025More people are dealing with norovirus this year for a couple of reasons. First, people dont have long-lasting immunity to norovirus. A 2013 study inEmerging Infectious Diseases found that immunity to norovirus may be as short as four years for adults, although some people may have protections for up to eight years.So, a bad bout in 2015 may remain strong in a persons memory, but by 2025, their immune system has likely forgotten the incident and lacks natural protections.The other reason norovirus is surging this year is because new strains have been introduced. Surges with up to 50 percent more illness occur in seasons during which a new strain emerges, Hopkins says.Starting in September, Hopkins says the U.S. saw the emergence of a new strain, genogroup II genotype 17 [P17]. Although the strain has been documented in other countries, it is new to the U.S., which means people here lack immunity.Regardless of whether a person comes into contact with the standard or new strain, the outcome will likely be the same. Most people who contract norovirus will experience symptoms for a few miserable days and then return to their regular lives.But the bug can cause serious complications and even death for young infants and older adults if they experience severe dehydration and circulatory collapse, Hopkins says.Norovirus vs. Food PoisoningAvoiding food poisoning means steering clear of undercooked, spoiled, or contaminated items. Prevention involves throwing out expired items, handling raw meat carefully and cooking items to the right temperature.However, avoiding norovirus involves a completely different plan of attack because it spreads through a fecal-oral route. This means a person with the bug sheds billions of microscopic particles when they experience diarrhea or vomiting.If the infected person fails to wash their hands properly, they can spread norovirus on surfaces ranging from a door handle to tongs sitting by a breakfast buffet. When the next person touches the door knob or the tongs, the virus spreads to their skin. If they touch their mouth or eat with their unwashed hands, they will ingest the virus and become infected themselves.The best advice to prevent the spread of norovirus is to wash hands well with soap and water, Hopkins says.People may also benefit from sanitizing surfaces with bleach-based cleaning products such as wipes or sprays. If a person does contract the bug, they will likely show symptoms between 12 and 48 hours. The symptoms can be similar to food poisoning, and only testing will determine whether a person has norovirus.Regardless of whether a person has food poisoning or norovirus, the care plan will be the same, hydration, rest, and time, Hopkins says.Article SourcesOur writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:National Foundation of Infectious Diseases. NorovirusEmerging Infectious Diseases. Duration of Immunity to Norovirus GastroenteritisCDC. How Norovirus SpreadsEmilie Lucchesi has written for some of the country's largest newspapers, including The New York Times, Chicago Tribune and Los Angeles Times. She holds a bachelor's degree in journalism from the University of Missouri and an MA from DePaul University. She also holds a Ph.D. in communication from the University of Illinois-Chicago with an emphasis on media framing, message construction and stigma communication. Emilie has authored three nonfiction books. Her third, A Light in the Dark: Surviving More Than Ted Bundy, releases October 3, 2023, from Chicago Review Press and is co-authored with survivor Kathy Kleiner Rubin.1 free article leftWant More? 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