An outbreak of stomach flu believed to be caused by norovirus has prompted a temporary shutdown of Babson College, a small business college and graduate school in Babson Park, Mass. School officials announced that classes, meetings, athletic events and all other activities would be canceled until Wednesday, when the school is expected to have the outbreak under control.

Dennis Hanno, Babson's undergraduate dean, says that 131 students have visited the school's health services clinic since Wednesday complaining of nausea, vomiting and diarrhea—all symptoms associated with norovirus, a group of viruses formerly known as Norwalk-like viruses. "We saw a high of 40 reported cases on Friday," Hanno told, noting that the numbers have dropped significantly since then with only four cases reported today. The main concern with this stomach virus, Hanno says, is that it may cause severe dehydration; 12 of the students received fluids intravenously to replenish those lost.

The virus is highly contagious. To avoid further transmission, Hanna says the school closed all congregating areas and instructed students to stay in their dorm rooms and avoid contact with others. The school is using bleach-based cleansers to scrub all surfaces—every last keyboard, mouse and door handle—in all common areas such as classrooms and dining halls. Students have also been given cleaning supplies to sanitize their own rooms and access to free laundry to clean all potentially contaminated clothing—and they are advised to wash their hands frequently.

"The students have been very cooperative," Hanno says. "I'm thankful the virus is one that is not life-threatening … but it has obviously created a lot of pain and discomfort in the community."

To get the lowdown on norovirus, we spoke with Mary Estes, a molecular virologist at Baylor College of Medicine in Houston.

[An edited transcript of the interview follows.]

What is norovirus?
It's actually a family of viruses that cause gastroenteritis [intestinal flu] in humans and some animals. The original norovirus was called the "Norwalk virus," after an outbreak of intestinal flu at an elementary school in Norwalk, Ohio, in 1968. But since that outbreak, researchers have come to realize that a number of viruses closely related to the Norwalk virus cause intestinal flu—together they are called the noroviruses. It's now "the cruise ship virus" because there have been so many outbreaks on cruise ships. It's the most common cause of nonbacterial intestinal flu. There are 23 million cases of norovirus annually in the U.S., according to the Centers for Disease Control and Prevention [CDC].

How do you catch it?
Norovirus is spread through the fecal-oral route, meaning that you get it by ingesting fecal matter from another person. You can get it by shaking hands with an infected person who didn't wash their hands after using the bathroom. But most likely, you would get it by eating food prepared by someone who hasn't washed his or her hands. You can also become infected putting your hand in your mouth after touching contaminated surfaces such as doorknobs, where the virus can probably be infectious for days.

Just because someone doesn't have active illness does not mean they can't pass the virus along to others. Studies show that people still excrete the virus's genetic material up to six weeks after they became infected, which probably means they can transmit it to others.

What kind of symptoms does it cause? Can it be deadly?
Symptoms begin about 24 to 30 hours after exposure, but they vary from person to person. You can have a lot of abdominal pain, vomiting and/or diarrhea. People that get both vomiting and diarrhea are really wiped; they're on the bathroom floor. Some people don't get any symptoms, probably because they have developed immunity from previous exposures. There is also a subset of people who seem to be resistant to infection by the virus, regardless of whether they have been exposed or not. We don't know the exact reason [why].

Anyone can die of severe dehydration, but norovirus is really only deadly among certain vulnerable populations: infants and the frail elderly.

Are there any treatments for norovirus infections?
There is no real treatment. The best advice is to drink a lot of fluids. If you keep rehydrating, most people get better in 48 to 72 hours.

What is the best way to avoid it?
Don't eat foods that are high-risk, such as oysters, which are sometimes harvested in water contaminated with human fecal matter. You should also wash your hands with hot water and soap before eating to prevent infection in yourself, and wash your hands after using the bathroom to keep from spreading it to others. We don't know if alcohol-based hand-sanitizers are effective, so it's safer to wash your hands.

Does norovirus affect other animals?
There is a norovirus in mice that causes encephalitis (inflammation of the brain), and researchers have found noroviruses that cause intestinal flu in pigs, cows and lions. So far, none of these animal noroviruses have been shown to infect humans.

Is norovirus becoming more common?

It's possible that there are more cases now than in the past because of the way food is prepared and distributed—one contaminated person at a restaurant or take-out service may be preparing food for hundreds of people in one night. But we have also gotten much better at detecting it, which might explain the apparent increase in numbers of cases reported. In 1990 researchers sequenced the virus's genome, and since then we have developed tests to detect the virus in a person's stool.