From VOA Learning English, this is the Health & Lifestyle report.

　　Everyone knows about the flu and the common cold. But what about norovirus?

　　If you have never heard of norovirus, you are not alone. Most people haven't.

　　The fact that people do not know its name does not mean it is rare. The virus is actually very common. Norovirus infects 700 million people each year, mainly in the developed world.

　　This video from the U.S. Centers for Disease Control and Prevention further explains the norovirus.

　　The virus is a very aggressive intestinal illness. It causes nausea, vomiting and the worst diarrhea most people have ever had. It is also a killer. More than 200,000 people a year die from this virus.

　　Medical costs linked to norovirus can be as high as $60 billion dollars a year. These costs include lost productivity at work because of personal illness or caring for a sick child. Because of this high price tag, health experts say norovirus is worth researching.

　　Bruce Lee is a professor of international health at the Johns Hopkins University Bloomberg School of Public Health. Lee and his colleagues estimated the cost of the illness in 233 countries, regions and territories around the world. He says norovirus is responsible for about 50 percent of all stomach and intestinal illnesses in those regions.

　　Lee and other researchers report their estimates in the journal PLoS One. Their calculations are thought to be the first regarding the global impact of norovirus.

　　Lee says that he and his team wanted to quantify -- or put into numbers -- and characterize the impact of the norovirus.

　　"We were interested in quantifying or better characterizing the impact of norovirus because it's something that you've heard of but if you think about it, you're not really sure what the impact, how often does it occur, how widespread is it."

　　In fact, Lee says, the actual number of people who get sick with norovirus may be much greater. Many people, he says, may just think they have a stomach bug when they actually have norovirus. A stomach bug is an informal way to describe something such as a germ that causes intestinal illness.

　　Again, here is Bruce Lee.

　　"So people may suffer with the symptoms and they think, 'well, I've got a stomach bug', quote-unquote, and 'I've got some food poisoning' and they never really report it or get diagnosed."

　　Lee hopes greater awareness will lead to control measures. These measures include washing hands and disinfecting food preparation areas. He adds that there is another important factor to consider: sick workers who still go to work.

　　When a worker is sick, he says, they often feel obligated to still go to work. This is especially true for people in food service jobs who may lose wages if they miss work. Sick people working around food can contaminate, or spread viruses to, many people. Sick workers instead, he says, should be encouraged to stay home.

　　"Many times, people who work in restaurants or the food preparation industry feel obligated to show up to work even though they're sick, because many folks are on wages and they can't afford to miss a day, even a day. And so, they'll come in sick and then they'll end up contaminating food and spread it to many other people."

　　There is currently no vaccine for norovirus. However, Lee says there are experimental vaccines under development. He says he hopes will one day a vaccine will help contain the spread of the virus.

　　I'm Anna Matteo.

　　In the Comments Section, practice using the words in this article relating to viruses.

　　Jessica Berman wrote this for VOA News in Washington, D.C. Anna Matteo adapted it for Learning English. Hai Do was the editor.