Noroviruses are members of a group of viruses called caliciviruses – also refered to as “Norwalk-like viruses.” Infection affects the stomach and intestines, causing an illness called gastroenteritis, or “stomach flu.”  The resulting inflammation of the stomach and intestines is not related to the flu (or influenza), which is a respiratory illness caused by influenza virus.

The symptoms of gastroenteritis include nausea, vomiting, and/or diarrhea accompanied by abdominal cramps. Some people also complain of headaches, fever, chills, and muscle aches.  Symtoms typically begin 24 to 48 hours after ingestion of the virus, but can appear as early as 12 hours after exposure. In turn, the resulting illness usually lasts for only 1 or 2 days. Although there is no evidence that infected individuals can become long-term carriers of the virus, it can remain in the stool and vomit of infected individuals for as long as 2 weeks after symptoms resolve.

Food and drinks can become contaminated with norovirus through contact with an infected person.  Food can be contaminated either by direct contact with contaminated hands or work surfaces that are contaminated with stool or vomit, or by tiny droplets from nearby vomit that can travel through air to land on food. Because the virus is so small, it takes relatively few norovirus particles to cause illness. Although the virus cannot multiply outside of human bodies, once on food or in water, it can cause illness.  Individuals can become infected with norovirus in several ways, including:

  • Eating food or drinking liquids that have been contaminated with norovirus;
  • Touching surfaces or objects contaminated with the virus, and then placing their hand in their mouth; and
  • Direct contact with another person who is infected and showing symptoms (for example, when caring for someone with illness, or when sharing foods or eating utensils).

Some foods can be contaminated with norovirus before being delivered to a restaurant or store. Several outbreaks have been caused by the consumption of oysters harvested from contaminated waters. Additionally, produce such as salads and frozen fruit may also become contaminated during harvesting and production.

People working with food who are sick with norovirus gastroenteritis are a particular risk to others, because they handle the food and drink many other people will consume.  A sick food handler can easily – without meaning to – contaminate the food he or she is handling. Many of those eating the contaminated food may become ill, causing an outbreak.

Most people recover completely within 1 to 2 days, with no long-term complications. In rare cases, however, persons who are unable to drink enough liquids to replace those lost from vomiting and/or diarrhea may become dehydrated and require special medical attention. These people include young children, the elderly, and persons unable to care for themselves.

As with most other pathogens, illness from norovirus can be easily avoided if proper hygienic and food handling procedures are followed.  Preventative Measures include:

  • Practice good hygiene, including thorough hand washing;
  • Disinfect potentially contaminated areas with a solution of detergent and chlorine bleach (sodium hypochlorite);
  • Routinely disinfect surfaces and furniture in common areas, such as lobbies and dining rooms. Where possible, allow bleach to stay on surfaces longer than 10 minutes;
  • Clean vomit with a two-step process: Collect visible debris with absorbent material, and then disinfect any surfaces that may have come in contact with vomit;
  • Avoid consuming raw shellfish, which may have been harvested from infected waters; and
  • Avoid contact sports if you have acute gastroenteritis;