(a group of viruses which are a common cause of gastroenteritis, or "stomach flu")

Getting to know noroviruses

A group of viruses that are a common cause of food poisoning and acute gastroenteritis ("stomach flu") which can strike quickly with force and make a person feel very sick, but which typically resolves within 2-3 days.

The characteristic symptoms are nausea, vomiting, diarrhea, and abdominal cramping. The diarrhea is not bloody. Fever, if present, is low-grade. Dehydration is the main complication, especially in infants and the elderly, and may need medical attention.

The clinical criteria for the diagnosis of norovirus infection include:

  1. An incubation period of 12-36 hours.
  2. An illness characterized by acute onset of nausea, vomiting, diarrhea, abdominal cramping, and, in some cases, fever and malaise.
  3. An illness of 12-60 hours duration.

The virus is spread primarily from one infected person to another by the fecal-oral route

Infected kitchen workers can contaminate a salad or sandwich as they prepare it, if they have the virus on their hands.

Infected fishermen have contaminated oysters as they harvested them and some raw oysters are now believed to be the cause of the virus depending on the degree of pollution of the water in which they grow. Eating raw oysters is NOT a good idea!

Norovirus infection has recently become a veritable plague on cruise ships.

Norovirus is named after the original strain "Norwalk virus" which caused an outbreak of gastroenteritis in a school in Norwalk, Ohio, in 1968.

Norovirus was coined to refer to the Norwalk-like virus by a simpler and more memorable term. It is now the official genus name for this group of viruses.

The illness caused by norovirus infection includes several names

  • Stomach flu; although this "stomach flu" is not related to the flu, influenza, which is a respiratory illness caused by influenza virus.
  • Viral gastroenteritis (an inflammation of the stomach and intestines), the most common name for an illness caused by norovirus.
  • Acute gastroenteritis.
  • Non-bacterial gastroenteritis.
  • Food poisoning; although there are other causes of food poisoning.
  • Calicivirus infection because of its characteristic "Star of David" shape with cup-shaped (chalice) indentations.

The seriousness of norovirus disease

Norovirus disease is usually not as serious as other illnesses, although people may feel very sick and vomit many times a day (and night); as well as, have diarrhea.

Most people get better within one or two days, and they have no long-term health effects related to their illness; however, some people are unable to drink enough liquids to replace the fluids they lose because after drinking, they immediately vomit and have a diarrhea.

The problem with dehydration is usually takes place with the very young, the elderly, and people with weakened immune systems.

How norovirous is spread to others

Noroviruses are found in the stool or vomit of infected people. Others can become infected with the virus in several ways:

  • Eating food or drinking liquids which are contaminated with norovirus.
  • Touching surfaces or objects contaminated with norovirus, and then placing a finger, or fingers, in the mouth.
  • Having direct contact with another person who is infected and showing symptoms; for example, when caring for someone with illness, or sharing foods or eating utensils with someone who is ill.
  • Food and drinks can very easily become contaminated with norovirus because the virus is so small and because it probably takes fewer than 100 norovirus particles to make a person sick.
  • Food can be contaminated either by direct contact with contaminated hands or work surfaces that are contaminated with stool or vomit.
  • Food or drinks can also be contaminated by tiny droplets from nearby vomit and can travel through the air to land on food.
  • Although the virus can not multiply outside human bodies, once on food or in water, it can cause illness.
  • Outbreaks of norovirus gastroenteritis have taken place in restaurants, cruise ships, nursing homes, hospitals, schools, banquet halls, summer camps, and family dinners.
  • Contamination takes place any where people have consumed water and/or food prepared or handled by others who have the virus.
  • It is estimated that as many as half of all food-related outbreaks of illness may be caused by norovirus.
  • In many of these cases, sick food handlers were thought to be the carriers of the norovirus.

So far, there is no evidence to suggest that an infected person can become a long-term carrier of norovirus; however, a person may pick up another variety of the virus.

There are many different noroviruses and being infected with one type does not prevent infection with another type later.

There are ways you can decrease the chances of being infected by norovirus

Everyone can decrease the chances of being contaminated with noroviruses by following the following preventive steps:

  • Make sure you wash your hands frequently; especially, after going to the toilet, if applicable, after changing diapers, and before eating or preparing food.
  • Carefully wash fruits and vegetables and steam oysters before eating them.
  • Thoroughly clean and disinfect contaminated surfaces immediately after an episode of illness by using a bleach-based household cleaner or an appropriate disinfectant.
  • Immediately remove and wash clothing or linens, with hot water and soap, which may be contaminated with the virus after an episode of illness.
  • Flush or discard any vomitus (matter from the stomach that has come up into and ejected beyond the mouth) and/or stool (excretory matter discharged in a bowel movement) into the toilet and make sure that the surrounding area is kept clean.
  • Food that may have been contaminated by a norovirus-ill person should be disposed of properly.
—Based on information provided by the
Centers for Disease Control and Prevention (CDC);
National Center for Infectious Diseases.

Additional virus words.