Known as the Norwalk virus, noroviruses were originally named after an outbreak that occurred at an elementary school in Norwalk, Ohio, in 1968. More than half the students and teachers became sick with diarrhea and vomiting, and contamination spread into the community. Four years later, Dr. Albert Z. Kapikian, using an electron microscope, identified a 27-nanometer virus-like particle in an infectious stool culture from the Norwalk outbreak and named the virus after the small town. Noroviruses are members of the Caliciviridae family of viruses that cause gastroenteritis, or an inflammation of the stomach and the large intestines. They are generally spread through contaminated foods, but can also pass from person to person. Indirect contact with contaminated objects and surfaces is also another way of transmission. Noroviruses are routinely considered a type of food poisoning, but not all infections are related to contaminated food.

What is the Name of the Illness Caused by Noroviruses?

The illness caused by a norovirus infection is known by several names. These include: food poisoning, calicivirus infection, stomach flu, winter vomiting disease, acute gastroenteritis, viral gastroenteritis, and acute non-bacterial gastroenteritis.

How Common are Noroviruses?

The National Institute of Allergy and Infectious Diseases (NIAID) reports that noroviruses are the most common cause of gastroenteritis outbreaks, causing about 23 million cases of illness each year. Some 50,000 cases require hospitalization and more than 300 deaths occur. The Centers for Disease Control and Prevention (CDC) reports that at least 50 percent of all food borne outbreaks of gastroenteritis can be attributed to noroviruses.

Are Noroviruses Just a Cruise Ship Problem?

No. Noroviruses easily spread in any environment where large numbers of people have close contact with each for a period of several days. Schools, hotels, daycare centers, nursing homes, hospitals, dormitories, and cruise ships are good examples. Why then does the public hear so much about norovirus outbreaks on cruise ships? Cruise ships are required by law to report any illness to the CDC, unlike hotels and resorts. Since the information is a matter of public record, the media have easy access.

How Do People Get a Norovirus Infection?

• Eating food or drinking liquids that are contaminated with noroviruses: In the United States, outbreaks are often traced to shellfish contaminated by raw sewage dumped in bodies of water, or to sick food handlers. Eating raw or under-cooked shellfish, especially oysters and clams, can be risky. Other foods most often implicated are salad ingredients and ready-to-eat foods.
• Noroviruses can spread from person to person through direct contact: Improper hand washing is one of the main causes of norovirus infections. Food handlers, hand shakers, and care givers can all spread the virus in this way. A study, using public bathroom monitors, showed that 50 percent of women and 75 percent of men leave restrooms without washing their hand, so think twice about shaking hands. Also, sharing a beverage, food, or utensil with an infected person can cause gastroenteritis to spread.
• Noroviruses also can spread through indirect contact: Noroviruses can survive on practically anything, including glassware, sinks, door knobs, and railings. Placing a hand in the mouth after touching contaminated surfaces and objects can result in infection. On cruise ships, the virus is typically spread way, as well as by physical contact with an ill person.

Are Noroviruses Contagious?

The virus is highly contagious and spreads easily from person to person, which is why noroviruses are implicated in large outbreaks. It is important to remember that people infected with noroviruses are contagious as soon as symptoms appear and for at least three days, often longer, after they recover. Anyone recovering from the virus should pay special attention to hygiene and wash hands frequently, since some people are contagious for as long as two weeks after they begin to feel better.

How Can I Prevent a Norovirus Infection?

• Thorough cooking of foods destroys the virus
• Thoroughly wash fruits and vegetables
• Never eat uncooked shellfish, such as oysters and clams
• Wash hands before eating or preparing food, particularly after changing diapers
• Wash hands frequently, especially when handling uncooked food and visiting the bathroom
• Disinfect all kitchen working surfaces regularly

Who is at Risk for a Norovirus Infection?

Anyone can become infected with this virus. It affects people of all ages. Extra care must be given to the elderly and the very young because dehydration is more common in these groups.

What are the Symptoms?

• Nausea
• Vomiting (possibly projectile)
• Diarrhea
• Abdominal cramps
• Headache
• Low-grade fever
• Muscle aches
• Fatigue

Symptoms usually develop 12 to 48 hours after exposure. The illness lasts only a few days, a little longer for the very young, the very old, and those with a challenged immune system, especially if dehydration is a factor. Although symptoms pass quickly, the illness can still be spread for days after symptoms disappear. Diagnosis of a norovirus infection is usually symptomatic, but can be confirmed through a stool sample. The technology to perform the test is not available everywhere, but the CDC and most state public health laboratories have the capability. Stool samples taken within 48 to 72 hours after onset of symptoms are best for detection.

How is a Norovirus Infection Treated?

There is no specific treatment for a norovirus infection and no preventative vaccine. Antibiotics are never prescribed for a viral infection. Most healthy people recover after a few days of sickness. Dehydration caused by diarrhea and vomiting can be a complication, so drinking plenty of fluids is a necessity. In serious cases, severe dehydration may require intravenous fluid replacement at a hospital.

Are There Any Long-term Effects?

No, there are no long-term effects from noroviruses.

How Can People Prevent the Spread of Noroviruses?

• Since noroviruses are so contagious, a person who is infected should try to stay away from others.
• People should be discouraged from visiting the home of a sick person.
• People should stay home from work while sick and for a few days after recovery.
• Proper hand washing by everyone is essential.
• Dishes and utensils of sick person should be washed separately with hot water and detergent.
• Laundry of sick person should be washed separately with hot water and detergent.
• Bathrooms should be cleaned and disinfected with bleach. Wear disposable gloves.
• Since noroviruses can become airborne when a sick person vomits, all surrounding surfaces should be sanitized.
• Thoroughly clean and disinfect contaminated surfaces immediately after an episode of illness by using a bleach-based household cleaner.
• Any food handled by a person with the virus should be thrown out.

Noroviruses in the News

1. February 2007: Bayview Seafood, a distributor in Seadrift, TX, issued a voluntary recall of oysters after 25 people experienced symptoms of a norovirus infection. The oysters were harvested from San Antonio Bay, TX.
2. December 2006: An Indianapolis Olive Garden restaurant was implicated in a norovirus outbreak blamed for making 370 people sick. Stool tests proved positive for noroviruses.
3. January 2006: Carrabba's Italian Restaurant in Lansing, Michigan, was the source of an outbreak. More than 400 diners became ill with a norovirus infection after eating at the establishment. The source was traced to sick employees and improper hand washing.
4. September 2005: A norovirus outbreak was reported among evacuees from Hurricane Katrina, staying at the Reliant Park in Houston, TX. Some 1000 people reported acute gastroenteritis.
5. October 2004: The Las Vegas Flamingo Hotel was the site of a major norovirus outbreak that caused more than 1200 guests and staff to become ill. The source of the outbreak was found to be sick employees.
6. March 2002: Nearly 200 people attending an Academy of Motion Pictures Award dinner at the Regent Beverly Wilshire Hotel in Beverly Hills, CA, became sick with a norovirus infection.
7. 1994-2007: Outbreaks on international cruise ships are numerous, as reported by the CDC.