The Latest Poop on Norovirus

“The overarching goal of managing a person with diarrhea is to maintain fluid and electrolyte balance to prevent the morbidity and mortality associated with dehydration and malnutrition.” Andi L. Shane, MD, et al., “Executive Summary: State of the Art Review: Infectious Diarrhea,” Clinical Infectious Diseases, November 2025

"The war on foodborne pathogens deserves the sort of national attention and resources that are devoted to the war on terror." Eric Schlosser, American journalist and food writer

I’m not sure what human pathogen is in the news most often, but I wouldn’t be surprised if it were norovirus—the leading cause of acute gastroenteritis (inflammation of the gastrointestinal tract) in the world and the number one cause of outbreaks of foodborne infection in the U.S. According to the Centers for Disease Control and Prevention (CDC), norovirus causes and average of 19-21 million illnesses, 109,000 hospitalizations and 900 deaths each year in the U.S. Recently, norovirus outbreaks at the Winter Olympics, on cruise ships and due to the consumption of contaminated seafood have captured the attention of the news media. In this week’s Germ Gems’ post, I highlight these recent outbreaks.

Norovirus infection: a recap. Named after Norwalk, Ohio, the city where it was discovered as a cause of an outbreak of diarrhea in 1968, noroviruses are a genetically diverse group of single-stranded RNA viruses. They are highly contagious. (Berg, S., “What doctors wish patients knew about the contagious norovirus.” AMA, January 24, 2025).

Noroviruses are transmitted by the fecal-oral route through contaminated food or water or by person-to-person contact. The virus may also be spread through air from the vomiting of an infected person when minute particles of vomit enter the mouth of another person. Because there are different serogroups or strains, a person can get norovirus illness many times in one’s life. Susceptibility to infection is determined in part by one’s genes.

A person usually develops symptoms 12 to 48 hours after exposure to norovirus. The most common symptoms of infection are non-bloody diarrhea, vomiting, nausea, stomach pain, fever, and headache. Diarrhea is more common in children and vomiting is more common in adults.

Norovirus illness can make you feel extremely sick. Vomiting and diarrhea can lead to dehydration, especially in young children and older adults. Symptoms of dehydration include extreme thirst, a dry sticky mouth and throat, decreased urination, and lightheadedness. It is crucial to keep a close eye on infants and older people for signs of dehydration. Evidence of dehydration in anyone with norovirus, however, should prompt medical contact.

There is no specific antiviral treatment for norovirus gastroenteritis. Generally, it takes a few days for the infection to run its course. It is important that during that time, a person take in enough fluids to prevent dehydration. Plain water works well but an electrolyte drink is worth considering if vomiting is prominent.

Norovirus outbreaks. The CDC defines a norovirus outbreak as the occurrence of “two or more illnesses (vomiting or diarrhea) resulting from a common exposure.” Norovirus outbreaks tend to be seasonal, overlapping with influenza (mistakenly called “stomach flu”), and are common in places where people are close together and touching the same contaminated surfaces, e.g., healthcare institutions, sports facilities, and cruise ships. Newsworthy outbreaks this year have included those occurring at the Winter Olympics, on cruise ships, or associated with certain foods.

The Winter Olympics. At this year’s Winter Olympics in Milan, Italy, Finland’s women’s hockey team was severely affected by norovirus. (The International Olympic Committee officials declined to call these cases an outbreak.) The Finnish squad was essentially wiped out. Over half of Finland’s roster was hit with the virus forcing postponement of Finland’s opening game against Canada.

The Canadian team went on to win the silver medal, and the American women’s hockey team won the gold. According to one source, strict hand hygiene played a crucial role in the U.S. women’s hockey team avoiding contracting the virus.

Norovirus outbreaks on cruise ships (2025-2026). Cruise ships account for only about 1% of the total U.S. norovirus outbreaks reported. Nonetheless, 2025 was a record-breaking year for gastrointestinal (GI) illnesses at sea and the norovirus was the cause of roughly 74% of the GI cases. The CDC reported there were 17 confirmed norovirus outbreaks on cruise ships during 2025. This was the largest number of cruise ship outbreaks in 12 years. (To qualify as an outbreak that requires mandatory reporting to the CDC, the voyage must have 3% or more of passengers or crew reporting symptoms of GI illness to the ship’s medical staff.) This increase was attributed to a new norovirus strain and an overreliance on hand sanitizer. (Hand sanitizer is less effective at stopping the spread of the virus than traditional handwashing with soap and water.)

Early 2026 reports suggest this will be another banner year of norovirus outbreaks on cruise ships. To date, 90 people (passengers and crew) became ill on a Holland America Caribbean cruise, 100 cases were confirmed during a long global voyage run by AIDA Cruises, and more than 25 people got sick on a Regent Seven Seas Cruise.

Foodborne Norovirus Outbreaks. Norovirus is the leading cause of disease from contaminated foods; it causes 58% of all U.S. foodborne illnesses. The virus is most commonly spread through food that is contaminated by infected handlers or during production due to contaminated surfaces. Foods that may be particularly affected are those that are eaten raw or undercooked. The top three risky foods are leafy greens (such as lettuce and spinach), fresh fruit (including berries), and shellfish (especially oysters). 

Lettuce and spinach are frequently implicated because they are often consumed raw and can be contaminated either in the field with fecal matter or by being washed in water containing fecal matter. Norovirus can contaminate fresh fruit, especially berries, if: (1) the water used to grow or raise the berries is contaminated; (2) the food handlers are infected and do not follow proper hygiene practices; (3) the fruit comes into contact with contaminated surfaces; or (4) individuals with the virus do not wash their hands before touching the fruit.

Shellfish like oysters and other mollusks (clams, mussels) are filter feeders that accumulate the virus from contaminated water. The top culprit for norovirus is oysters-- particularly when eaten raw or undercooked. On February 18, 2026, the U.S. Food and Drug Administration issued an advisory to restaurants and retailors not to serve or sell certain oysters from British Columbia because of norovirus contamination.

Prevention of Norovirus. No licensed vaccines exist for norovirus despite its status as a leading cause of epidemic and endemic gastroenteritis globally. Several biotechnology companies and academic centers, however, have vaccines that are in advanced stages of development. As of February 2026, the key player seems to be Moderna with an mRNA-based vaccine.

In the absence of a high tech solution, everything is about preventing getting the norovirus in the first place and behavioral measures are the mainstay of prevention. Therefore, wash your hands properly with soap and water. Stay at home if you are sick. Sanitize frequently touched surfaces as an infected person can transmit norovirus for up to two weeks after they are well. (The U.S. Environmental Protection Agency has a list of disinfectants that are active against norovirus.) To prevent foodborne norovirus, rinse fruits and vegetables with clean running water and cook shellfish thoroughly.

Given the critical role of proper handwashing with soap and water in the prevention of norovirus infection, I highly recommend that everyone watch the CDC’s on-line video “Fight Germs, Wash Your Hands!” periodically, and certainly before your next voyage on a cruise ship.

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