What Is Norovirus?

world's largest cruise ship
(Image credit: Royal International Caribbean)

Norovirus is a very contagious virus that causes gastrointestinal illness in humans. It is the most common cause of illnesses from contaminated food in the United States — an estimated 20 million Americans get sick with the virus each year, according to the Centers for Disease Control and Prevention (CDC), and it is blamed for as many as 800 deaths in the United States each year.

Norovirus is named for Norwalk, Ohio, where the first confirmed outbreak was recorded, in 1968. People sometimes refer to a norovirus infection as "stomach flu," even though the virus is not related to influenza.

How norovirus spreads

The notoriety of norovirus comes from the ease with which it spreads from one person to another: You can catch it by ingesting food or drink that's been contaminated, or by touching any contaminated surface, then touching your nose, mouth or eyes. The virus is also aerosolized, or sprayed into the air, when an infected person vomits or flushes a toilet, and can spread when a person inhales the aerosolized virus.

And it does not take much to get a person sick — as few as 18 virus particles on a person's hands or in their food can make them sick, according to the CDC. (The number of norovirus particles that fit on a pinhead would be enough to infect more than 1,000 people, the CDC said.)

Norovirus is well-known for causing outbreaks on cruise ships. Indeed, the close quarters of a cruise ship make it easy for the virus to spread from person to person.

But outbreaks on cruise ships actually account for only 1 percent of all norovirus outbreaks, according to the CDC. Most of the outbreaks of foodborne illness from the virus get started in restaurants, the CDC said. And CDC research has found that, of the norovirus outbreaks involving contaminated food, 70 percent are caused by infected food workers. This can happen when a food service worker is sick with the virus and prepares food for customers.

Symptoms of norovirus

Norovirus symptoms generally begin within a day or two of exposure. The effects include nausea, vomiting, diarrhea, and stomach pain and cramps. In some cases, victims also suffer fever, chills, headache, weight loss and fatigue.

Though these symptoms can be severe, they are usually short-lived, and most people recover within two days. Only particularly severe cases, usually involving young children, the elderly or people with compromised immune systems, require hospitalization.

Though the symptoms may end quickly, an infected person can continue to shed the virus, or infect other people with it, for up to three days after recovery, according to the CDC. This is another factor that makes a norovirus outbreak so tough to control.

Treatment and prevention

There isn't a specific treatment for norovirus infection — most cases usually resolve on their own in a few days And because it's a virus, you can't treat it with antibiotics.

Sports drinks and rehydration drinks can help replace fluids lost by diarrhea and vomiting. Though a vaccine for norovirus is in development, it has not yet been approved.

The best way to prevent a norovirus infection — on a cruise ship or elsewhere — is through careful handwashing and good general hygiene. Eat only foods that have been properly handled and prepared, and avoid raw shellfish and undercooked seafood.

If you have been infected with norovirus, do not prepare food for others for at least two days after you recover, the CDC recommends. Carefully wash any potentially contaminated laundry; clean toilets, other bathroom surfaces and all kitchen areas with a bleach-based solution.

Original article on LiveScience.

Live Science Contributor
Marc Lallanilla has been a science writer and health editor at About.com and a producer with ABCNews.com. His freelance writing has appeared in the Los Angeles Times and TheWeek.com. Marc has a Master's degree in environmental planning from the University of California, Berkeley, and an undergraduate degree from the University of Texas at Austin.