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  • Writer's pictureP.K. Peterson

Outbreaks of “Winter Vomiting Disease” (Norovirus Infection) Are on the Rise

“Our finding of a relatively high burden of morbidity and mortality attributed to norovirus outbreaks in LTCFs [long-term care facilities] aligns with previous research.”

- Laura E. Calderwood, MPH and Sara A. Mirza, Ph.D., MPH, Centers for Disease Control and Prevention

“Life is better with clean hands.”

- Centers for Disease Control and Prevention Handwashing Campaign

Norovirus is the leading cause of acute gastroenteritis in the world. An estimated 685 million cases occur annually with about 200 million in children under 5 years old resulting in 50,000 child deaths every year. While most of the havoc norovirus causes is suffered in developing countries, in the U.S., norovirus causes 19 to 21 million cases of vomiting and diarrhea annually precipitating 109,000 hospitalizations. In early January of this year, the Centers for Disease Control and Prevention (CDC) warned that outbreaks of norovirus illness are on the rise. In this Germ Gems post I shine light on norovirus with the aim of promoting the single most important means of prevention—handwashing with soap and water.

Overview of norovirus and the disease it causes. 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. The genus Norovirushas one species that is called Norwalk virus. Noroviruses are classified into at least seven different genogroups. Most noroviruses that infect humans belong to two serogroups (GI and GII).

Noroviruses are highly contagious. They’re usually 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. Because there are many 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 norovirus infection are diarrhea, vomiting, nausea, stomach pain, fever, and headache. Diarrhea is more common in children, and vomiting is more common in adults. Because vomiting is a common symptom and most cases of norovirus occur between November and April, norovirus infection is often referred to as “winter vomiting disease.” Given its overlapping seasonality with influenza, it is sometimes called “stomach flu.” (Although influenza can cause gastrointestinal symptoms, most cases of vomiting and diarrhea in the winter are caused by norovirus.)

Norovirus illness can make you feel extremely sick, and vomiting and diarrhea can lead to dehydration, especially in young children and older adults. Symptoms of dehydration include decreased urination, dry mouth and throat, and feeling dizzy when standing up. Evidence of dehydration should prompt medical contact.

Epidemiology. In 2012, the CDC established the Norovirus Sentinel Testing and Tracking Network (NoroSTAT) in collaboration with 12 state health departments. In April 2020, the incidence of norovirus outbreaks in the U.S. declined substantially, likely due to implementation of COVID-19-related nonpharmaceutical interventions such as social distancing and increased handwashing. Starting in January 2023, however, norovirus outbreaks increased rapidly and are now approaching pre-COVID-19 pandemic levels.

Norovirus outbreaks are common in places where people are close together and touch the same surfaces, for example, in day care centers and on cruise ships. (Cruise ship outbreaks, however, represent less than 1% of all outbreaks.) In September 2022, the CDC reported the largest outbreak of acute gastroenteritis, which was documented in the Grand Canyon National Park backcountry among 222 rafters and backpackers and related the outbreak to decreased access to hand hygiene.

In the U.S., norovirus is the leading cause of healthcare-associated gastroenteritis. During 2009-2018, 50 states, Washington, D.C., and Puerto Rico reported 13,092 norovirus outbreaks and 416,284 cases in long-term care facilities (LTCF). Most LTCF outbreaks were spread person-to-person.

Norovirus is also the leading cause of disease from contaminated foods. Foods that are commonly involved are leafy greens, fresh fruits, and shellfish (such as oysters). Last year two large norovirus outbreaks occurred in people who consumed raw oysters linked in one outbreak to oysters originating in British Columbia and in the other from raw oysters harvested in Galveston Bay, Texas.

How do you treat norovirus infection? There is no specific antiviral treatment for norovirus gastroenteritis. Generally, you just need a few days to let the infection run its course. But it’s important to get enough fluids to prevent dehydration. Plain water works well but an electrolyte drink is worth considering if vomiting is prominent. It’s recommended to keep a close eye on infants and older people who are vomiting— if they are lethargic it could be a sign of dehydration.

In addition to other viruses, a number of bacterial pathogens can cause gastroenteritis. Seeking medical attention should be considered if diarrhea is associated with bloody stools or high fever or severe abdominal pain, which may point to bacterial gastroenteritis.

How do you prevent getting norovirus infection. Given a global burden of more than 200,000 deaths and an economic cost of more than $60 billion each year, it’s not surprising that several pharmaceutical companies are developing vaccines to target norovirus. But as vaccines are not yet available, behavioral measures are the mainstay of preventing norovirus infection. These measures include washing fruits and vegetables thoroughly before eating, cooking seafood to at least 63C (145F), and sanitizing shared surfaces if someone in your household is infected.

In the absence of a high-tech solution, the single most effective way to prevent norovirus infection is already known and taught by most parents to their children: “Wash your hands with soap and water.” The CDC has a video on how to wash one’s hands properly.

The CDC also provides guidance regarding proper handwashing on their website “Handwashing in Communities: When and How to Wash Your Hands.” The CDC recommends that you “wash your hands with soap and water for at least 20 seconds. Use the cleanest water possible, for example from an approved source. If soap and water are not available, use an alcohol-based hand rub that contains at least 60% alcohol”

We would all like to “wash our hands” of norovirus. So, even if your parents did get it right, I recommend watching the CDC’s video on the proper way to wash one’s hands. It is the single most important way of preventing the spread of this virus.

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Main Page images courtesy of Shuxian Hu, MD. Dr. Hu is a scientist in the Neuroimmunology Research Laboratory at the University of Minnesota.

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